A US research firm's allegations of fraud against billionaire Gautam Adani's business empire have sparked a political row in India.

Opposition leaders stalled the functioning of parliament for a second straight day on Friday as they demanded an investigation into the claims.

The research firm accused Adani group firms of stock manipulation and financial fraud last week, sending its shares into a sharp fall.

The group has denied the allegations.

On Friday, morning sessions in both houses of India's parliament were adjourned as opposition leaders demanded an investigation.

They have called for a Joint Parliamentary Committee or a Supreme Court-monitored panel to be set up to investigate the allegations against the firm and the risk to Indian investors from the fall in Adani company shares.

The Adani group's companies have seen $108bn wiped off their market value over the past few days after US-based investment firm Hindenburg Research published a report accusing it of decades of "brazen" stock manipulation and accounting fraud.

The group has dismissed the allegations as malicious and untrue, calling them an "attack on India". But the response has failed to stop the fall in Adani shares.

Gautam Adani, the founder, has fallen out of the top 10 richest in the world. According to the Forbes real-time billionaires list, Mr Adani is now the 15th-richest person in the world, with a net worth of $74.7bn. He was third on the list last week.

The billionaire runs Adani Group, one of India's biggest companies. The flagship company, Adani Enterprises, has operations in a wide range of industries including commodities trading, airports, utilities and renewable energy.

Opposition lawmakers had disrupted parliamentary proceedings on Thursday as well, after their notices to suspend business to discuss the Adani issue were rejected by the government.

"There should also be day-to-day reporting of the investigation on the issue," Mallikarjun Kharge, chief of the main opposition Congress party, said.

The Congress has also accused the government of forcing the State Bank of India (SBI), a public-sector bank, and government-owned insurance company, Life Insurance Corporation of India (LIC), to invest in the firm, jeopardising people's savings.

But on Friday, India's finance minister Nirmala Sitharaman, quoting earlier statements made by SBI and LIC, told a news channel that the exposure of the two companies to the Adani group was "well within the permissible limits".

She also said that India's financial market was "well-regulated" and that investor confidence would not be shaken.

The Congress has also announced plans to hold nationwide protests outside the offices of Adani Group companies, nationalised banks and public institutions on Monday.

Party leader KC Venugopal has accused the BJP-led government of "using common people's money to support their closest friends".

Mr Adani is perceived as being close to Prime Minister Narendra Modi and has long faced allegations from opposition politicians that he has benefited from his political ties, which he denies.