Demonstrators listen to speakers at a rally against taking military action against ISIS in Syria, held outside Downing Street in London, November 28, 2015.

British defense minister Michael Fallon said on Sunday the government wanted to have a vote in parliament to launch air strikes against Islamic militants in Syria this week but it had to keep building the case of extending military action.

Asked whether there would be a vote in parliament this week, Fallon said: “We’d like to have a vote for military action but we’ve got to keep building the case.”

But Fallon said Britain was not certain of holding a parliamentary vote, as it would become “difficult” if opposition leader Jeremy Corbyn ordered his MPs to oppose it.

Asked whether the government had got the votes needed to get parliamentary approval for the air strikes, Fallon told the BBC’s Andrew Marr Show: “Not yet, we are working at it and we need to keep working at it.”

He had previously said in an interview published in the Sunday Telegraph, that he hoped lawmakers from all parties would consider the arguments.

Labour leader Corbyn wants his lawmakers to vote against air strikes. But many of his MPs, including some in his top team, are demanding a free vote rather than one in which they are directed to vote against the strikes.

With a slender majority, Conservative Prime Minister David Cameron wants MPs outside his party to back extending air strikes to hit Islamic State in Syria. Britain has already carried out air strikes targeting ISIS in Iraq.

Cameron’s drive to win support in parliament has taken on fresh urgency after the Nov. 13 attacks in Paris in which 130 people were killed. Islamic State claimed responsibility for the attacks.

Asked if a vote on action in Syria was certain to go ahead, Fallon said: “No. We are committed to building a consensus, seeing whether there is a majority there.”

Fallon added that it would “certainly make it more difficult” if Corbyn directed his MPs to vote against action in Syria.

Cameron lost a 2013 vote in parliament on carrying out air strikes against Syrian President Bashar al-Assad’s forces. On that occasion, Labour did not give its lawmakers a free vote and ordered them to vote against the government.

Former Labour Prime Minister Tony Blair’s decision to join the U.S.-led Iraq war in 2003, in which 179 British service personnel were killed, remains contentious in Britain after questions were raised over intelligence that was used to justify the invasion.

Corbyn came under further pressure this weekend to allow his MPs to vote freely on military action after his deputy leader Tom Watson told the Independent he favored a free vote. Finance spokesman John McDonnell, one of Corbyn’s closest allies, has also backed a free vote.

Most Labour lawmakers did not support Corbyn’s leadership bid but he was backed by an overwhelming majority of grassroots party members.

An opinion poll released on Friday indicated 48 percent of British voters supported extending air strikes to hit ISIS in Syria, with 30 percent opposed.

The poll, conducted by polling firm Survation for the Daily Mirror newspaper, also showed 49 percent favored diplomatic and non-military options before committing Britain to anything more than air strikes.

Related articles across the web

• Bashar al-Assad Had a Great InstaSummer While His People Drowned in the Mediterranean
• President al-Assad the only guarantee for Syria's stability, Czech MEP asserts
• French FM: If We Want Assad Down, We Won't Get Far
• Not Losing Face in Syria
• The Syrian Powder Keg: Markets Getting Explosive
• Obama Officials Slam British PM For His Gross "Incompetence" In Handling Syria Crisis...
• Unclear if US-Russia interests overlap in Syria - Pentagon
• China ready to send troops to Syria if the Assad regime is threatened
• Netanyahu, Putin Aim to Prevent Accidental Israeli-Russian Clashes in Syria
• Israeli, Russian Deputy Military Chiefs to Coordinate on Syria