Indian university student Niranjana Santhosh was so close to being evacuated from the bombarded Ukrainian city of Sumy on Monday that she was sitting on a bus with her bags packed, waiting for the driver to start the engine.

But three hours later, she and dozens of other Indian students who had hoped to be ferried to a safer city, away from Russian attacks, received a WhatsApp message from the Indian embassy with devastating news.

A temporary ceasefire negotiated between Russia and Ukraine to allow civilians to flee four cities, including Sumy, had failed.

"We are so sad and desperate," Santhosh, who left the bus to return to the hostel above the dank, dark bunker where hundreds of students have huddled for days with little food and no electricity. Some are so thirsty they're melting snow to drink.

Indian students in Sumy have run out of water, they are collecting snow to drink.

The failed evacuation raises pressure on Indian Prime Minister Narendra Modi to bring the students home as anger grows and Russia's invasion intensifies with attacks on residential and civilian targets.

Modi spoke with both Russian President Vladimir Putin and Ukraine's President Volodymyr Zelensky on Monday about the students' plight, according to a statement from the Indian Ministry of External Affairs.
Russia claims it is willing to cease its offensive, and open corridors to allow citizens to leave a small number of cities, including Sumy. However, Ukraine has rejected that on the basis Ukrainians would be evacuated to Russia or its ally Belarus and would require people to travel through active areas of fighting.
Ukrainian and Western leaders have also accused Russia of repeatedly sabotaging rescue efforts by continuing to target pre-approved safe routes. On Sunday, a Russian strike hit an evacuation crossing point outside Kyiv, killing eight people including two children trying to flee.
In Sumy, the Indian students -- like millions of Ukrainians in cities across the country -- are growing increasingly desperate to escape Russia's attacks.
"I'm mentally exhausted," Santhosh said. "We are just living with hope."
On Tuesday, Indian Cabinet Minister Hardeep Singh Puri said the evacuation of all students in Sumy to Poltava, a city 100 miles away, was underway. "As we are speaking the evacuation is going on," Puri told reporters Tuesday evening Indian local time.

Niranjana Santhosh, right, pleads for help to evacuate Indian students from Sumy, Ukraine.

Uncertainty and fear
Merlyn Shebu arrived in Ukraine just over two months ago, excited about studying her first year of medicine at Sumy State University.
But for nearly two weeks, she's been sheltering with other students in a dusty bunker beneath their hostel. Sewage water flows through the cold and damp room and fungus grows up the walls. There are no toilets, and students have no place to even sleep on the uneven concrete floor in freezing temperatures.
"We are in a desperate situation. We don't know who will come and help us," 21-year-old Shebu told CNN last week. "Please evacuate us soon before our life ends here."

Merlyn Shebu, pictured in her lab coat before the war, was excited at the prospect of becoming a doctor.

More than 2,000 international students from 27 countries, including China and Turkey, remain stranded in Sumy, according to a tweet from Ukrainian lawmaker Lesia Vasylenko posted Tuesday.
She said Russian had refused a "green" corridor and told the students to "hold tight, #Ukraine army will be there soon."
The Indian students who spoke to CNN from Sumy say they are studying in Ukraine because many of them didn't qualify for the limited places at Indian medical schools, and university fees in Ukraine are significantly cheaper than private universities in India.
According to data from UNESCO, more than 14,000 Indians are currently enrolled in Ukraine universities -- the single largest group of foreign students in the country.
Now only about 700 remain, according to the Indian government. Most are in Sumy -- Indian students in other cities were advised to leave Ukraine as tension built before the invasion.
"I think we will go back to India only after we die," 23-year-old medical student Mahtab Raza told CNN from Sumy last week, his voice quivering in fear.
"We have been imploring the government to rescue us for days. Everyone is crying, everyone is scared."
On Saturday, a group of students became so desperate to leave they threatened to walk 37 miles (60 kilometers) to the Russian border, braving Russian gunfire and damaged roads and bridges.
"If anything happens to us, all the responsibility will be on the Indian embassy," Mariya Munaf, a 22-year-old student, said on a video message as she stood with at least 100 students, some holding Indian flags.
CNN contacted the Ministry of External Affairs multiple times to ask what was being done to evacuate the students in Sumy but officials declined to comment.

Indian students in Sumy say they will risk their life and walk to the Ukraine-Russia border to be evacuated.

'I survive on water'
The Indian government issued urgent advisories for nationals to evacuate Kyiv and Kharkiv on February 15 and make their way to the western Ukrainian border.
But the students in Sumy say they weren't given clarity about their situation -- until Saturday. Calls to the Indian embassy's helpline went unanswered for days, they said.
They fear either dying in their bunker or being shot outside, like another Indian student, Naveen Gyanagoudar, who was killed by Russian shelling last week while buying groceries in the city of Kharkiv.
"After Naveen's death, I started eating once a day," said Shweta Raj, a 22-year-old medical student. "What if something happens to me while I'm standing in line (to get food)? So I eat once a day. I eat very little. I survive on water."

Mahtab Raza, pictured with several other Indian students, are desperate to leave Sumy.

Back home in India, Gyanagoudar's death sparked political debate. Opposition parties criticized the Indian government's evacuation efforts, saying they needed to be better planned.
Some repeated demands from the West for India to take a stronger stand against Russia. So far, Delhi has abstained from voting on multiple UN Security Council resolutions demanding Moscow stop its attack on Ukraine.
Delhi has been reticent to condemn Russia due to its defense ties with Moscow, according to Donald Lu, the US Assistant Secretary of State for the Bureau of South and Central Asian Affairs.
India relies on Russia for at least 50% of its military equipment -- a relationship given an increased level of importance in recent years owing to India's fraught relationship with neighbors Pakistan and China.
At the same time, India is a member of Quad -- an informal defense alliance with the United States, Japan and Australia -- who have all imposed sanctions against Russia.
"All of us have been working to urge India to take a clear position, a position opposed to Russia's actions. But what have we seen so far? We have seen a number of abstentions," Lu said during a Senate subcommittee hearing about US-India relations on March 2.

Mahtab Raza along with several other Indian students in an underground bunker in Sumy.

Modi has appealed to Putin for a "cessation" of the violence -- but has fallen short of condemning his unprovoked attack. India has also pledged humanitarian aid to Ukraine and Modi has spoken with Zelensky about the crisis.
Last week, as pressure mounted on Modi, some of his supporters questioned why Gyanagoudar had ignored the government's advisories to leave and whether he was waiting for a "private jet" to bring him back.
In a speech on February 26, before Gyanagoudar's death, Modi himself questioned why Indian students go abroad for studies, although he didn't directly refer to the Ukraine crisis.
"Our students today are going to small countries, especially for medical education. Language is a problem there... large sums of Indian money is going abroad," he said.

His comments struck a nerve with some students stranded in Ukraine, who say they feel betrayed by his response.
"How can you say that Prime Minister? how can you say that?" Raj, the first-year medical student said. "We were looking forward to you (helping us), and you just said why (do) we go?"
On Monday, T. S. Tirumurti, India's Ambassador to the United Nations, emphasized India's desire for a peaceful outcome in Ukraine.
"India has been consistent in calling for an immediate end to all hostilities," Tirumurti said.
"We have also reiterated our urgent demand for safe and uninterrupted passage for all innocent civilians including Indian nationals remaining in Ukraine. We're deeply concerned that despite our repeated urgings to both sides, the safe corridor for our students stranded in Sumy did not materialize."
On Tuesday, Ukraine and Russia agreed a single corridor to allow civilians to evacuate Sumy south via Holubivka and Lokhvytsia to the city of Poltava. "We call on Russia to agree on these routes immediately and ensure a stable ceasefire on these routes," Iryna Vereshchuk, Ukraine's minister of Reintegration of Temporarily Occupied Territories said in a statement.
Indian embassy officials are waiting stationed in Poltava to help with the evacuation, the embassy said on Twitter Sunday.
But the students fear they are running out of time.

"Please don't let another Naveen die," Raj said. "It is very scary, we are away from our parents and no one is here to protect us."