Image copyright Getty Images Image caption Mr Shkreli said he would remain silent if forced to appear at the hearing

Former Turing Pharmaceuticals CEO Martin Shkreli has asked for immunity in order to testify before a US congressional hearing.

He was subpoenaed to testify about a 5,000% price increase for a drug.

Reuters reported that Mr Shkreli's lawyer asked for immunity because of an ongoing Federal Trade Commission (FTC) investigation into the price rise.

Mr Shkreli stepped down as Turing's head following his arrest for investor fraud at a different company.

In a letter seen by Reuters, Mr Shkreli's lawyer said the former CEO would "gladly cooperate" and produce documents at the hearing next Tuesday if he is given immunity.

On Thursday, Mr Shkreli said he would remain silent if forced to appear at the congressional hearing.

The FTC is allegedly investigating anti-trust violation by Turing Pharmaceuticals when it raised the price of the drug Daraprim.

Daraprim is used to treat toxoplasmosis, an infection common in people with Aids. The drug was invented in the 1950s and acquired by Turing for $50m (£35m) in 2015. In August, Turing increased Daraprim's price from $13.50 to $750 per dose.

Fraud charges

In December, Mr Shkreli was arrested in New York on charges he defrauded investors as the head of drug company Retrophin and as a fund manager at the hedge fund MSMB Capital Management.

He has denied the charges and was released on bail pending the trial.

Image copyright Getty Images Image caption Martin Shkreli was arrested in December for investor fraud

Members of the House of Representatives Oversight Committee have argued Mr Shkreli cannot invoke his right against self-incrimination because his arrest is separate from the congressional investigations.

They have responded angrily to Mr Shkreli's attempts to avoid testifying.

On Thursday, Congressman Elijah Cummings, a committee member, said: "If he plans on trying to use his own intentional inaction as some kind of bogus excuse for not showing up at Tuesday's hearing, people will see right through such a juvenile tactic."

Mr Shkreli has mocked the subpoena on social media. He tweeted a picture of the letter sent by the Oversight Committee with the comment "Found this letter. Looks important."