Image copyright Reuters Image caption Canadian Prime Minister Justin Trudeau is under pressure for his handling of the SNC-Lavalin affair

Canadian Prime Minister Justin Trudeau has denied wrongdoing after he tried to shield one of the country's biggest firms from a corruption trial.

Mr Trudeau said any lobbying by him or his inner circle for engineering giant SNC-Lavalin was done to protect jobs.

In explosive testimony, ex-Justice Minister Jody Wilson-Raybould said she faced "sustained" pressure to abandon prosecution of the Quebec-based firm.

Opposition Conservatives are calling on the Liberal PM to resign.

They are also demanding a public inquiry following Ms Wilson-Raybould's testimony on Wednesday before the Commons justice committee in Ottawa.

How did Trudeau defend himself?

Speaking to reporters on Thursday morning, Mr Trudeau said he disagreed with his former justice minister's "characterisation" of events and maintained his staff followed the rules.

The prime minster said he had full confidence in an inquiry by a parliamentary justice committee into the affair and in an investigation by the federal ethics commissioner, and would "participate fully" in that process.

Opposition parties have been ramping up pressure on the prime minister and the Conservatives have said the Royal Canadian Mounted Police must immediately open an investigation.

Mr Trudeau said that to his knowledge no member of his staff has been contacted by the RCMP.

The prime minster has insisted for weeks that all communications between himself, federal officials and Ms Wilson-Raybould were above board.

He says that any advocacy for SNC-Lavalin was done in the interest of protecting Canadian jobs that no lines were crossed.

What does the ex-justice minister allege?

Ms Wilson-Raybould told the justice committee on Wednesday she had faced attempts at interference and "veiled threats" from top government officials seeking a legal favour for the Montreal construction firm.

The former justice minister and attorney general said she and her staff endured four months - between last September and December - of a "sustained" and "inappropriate effort" to push for a possible deferred prosecution agreement for the construction company.

That agreement would have allowed the firm to avoid a criminal trial and instead agree to alternative terms or conditions, like penalties or enhanced compliance measures.

Ms Wilson-Raybould said that while some discussions about the ramifications of the decision were normal, the pressure went well beyond what was appropriate given her role as attorney general.

In Canada, an attorney general is supposed to act independently with respect of his or her prosecutorial function and decisions are not supposed to be politically motivated.

Ms Wilson-Raybould said that in various meetings, Mr Trudeau and senior staff repeatedly raised concerns about the possibility of job losses and potential political ramifications of a trial.

She said she had made clear she was not prepared to help the company avoid a trial and that she believes it was why she was demoted in a Cabinet shuffle in January, which Mr Trudeau denies.

Ms Wilson-Raybould also said during her testimony she did not believe any laws were broken.

What is SNC-Lavalin accused of?

The company and two of its subsidiaries face fraud and corruption charges in relation to about C$48m ($36m; £28m) in bribes it is alleged to have offered to Libyan officials between 2001-11.

The firm has openly lobbied to be allowed to enter into a remediation agreement instead of going to trial, saying it has cleaned house and changed its ways.

SNC-Lavalin and its supporters say it would be unfair to penalise the company as a whole and its thousands of employees for the wrongdoings of former executives.

Preliminary hearings have begun and the company says it will "vigorously defend itself" against the allegations.

A conviction on fraud and corruption charges could result in a decade-long ban on bidding on federal contracts, which would be a major financial hit for the firm.

What's the company background?

SNC-Lavalin is one of the world's largest engineering and construction companies and employs some 9,000 people in Canada.

The firm has deep roots in the vote-rich province of Quebec, which is expected to be a battleground in this October's general election.

This is not the first time SNC-Lavalin has found itself in trouble.

In 2016, the agency that oversees Canadian federal elections said former executives had devised a scheme to illegally donate C$118,000 to the federal Liberals and Conservatives between 2004-11. The bulk of the funds went to the prime minister's Liberal Party.

In 2013, the World Bank barred the firm and its affiliates for up to 10 years from bidding on contracts with the agency for "misconduct" in a bridge contract in Bangladesh, the longest debarment period ever handed down in a settlement.

How bad is this for Trudeau?

Political commentators suggest Ms Wilson-Raybould's remarks are deeply damaging for Mr Trudeau and the Liberals.

Writing in the Toronto Star, columnist Chantal Hebert says the prime minister was "already up to his neck in the SNC-Lavalin mess".

"On Wednesday, former attorney general Jody Wilson-Raybould pushed his head down further. It will be harder for the Liberal government to dig itself out of the deep hole she dug before the next campaign."

In the National Post, columnist Andrew Coyne said Ms Wilson-Raybould's testimony suggested "an attitude that appears to pervade this government: that the law is not an institution to be revered, but just another obstacle to get around, by whatever means necessary."

Columnist Patrick Lagace, writing in Montreal newspaper La Presse, said her remarks suggest that "for the Prime Minister and people acting on his orders, the rule of law and the independence of the Attorney General were at least negotiable".

In Maclean's magazine, Paul Wells suggests her remarks reveal a "sickeningly smug protection racket whose participants must have been astonished when she refused to play along".