By Kylie MacLellan
LONDON (Reuters) - British Prime Minister David Cameron will this week set out the case for joining air strikes against Islamic State militants in Syria, his finance minister said on Sunday, in a bid to persuade a parliament loath to embark on another war in the Middle East.
Britain is already bombing IS in Iraq but Cameron has said he believes Britain should be doing more to fight the militants, who claimed responsibility for this month's attacks in Paris in which 130 people died.
France has in the days since stepped up its bombing campaign against the group's members in Syria, who are also being targeted from the air by a U.S.-led coalition and Russia.
Cameron is keen to avoid a repeat of 2013 when he lost a crunch parliamentary vote on air strikes against Syrian President Bashar al-Assad's forces.
"The prime minister will seek support across parliament for strikes against that terrorist organization in Syria. Frankly Britain has never been a country that stands on the sidelines and relies on others to defend us," finance minister George Osborne told BBC television on Sunday.
"The timetable is this: In the coming week the prime minister will come to the House of Commons ... we will make the case as a government, we will allow MPs to digest that response and then we will see where we stand."
Britain's Sunday newspapers, carrying headlines including "Britain prepares for war", reported a vote could be held within the next two weeks, with bombing underway by Christmas.
Osborne said the Paris attacks were likely changing the views of those previously opposed to British air strikes but said the government would only call a vote when it was confident it could win. Another defeat would be "a publicity coup" for IS and send "a terrible message about Britain's role in the world", he said.
Cameron has said his bid to join the U.S.-led coalition in Syria was strengthened by Friday's United Nation Security Council resolution to redouble action against Islamic State there.
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 a contentious issue in Britain.
Some in Cameron's own Conservative Party are opposed to air strikes, so the British leader will need to persuade some opposition Labour lawmakers to back his call for action.
Labour leader Jeremy Corbyn, who opposes air strikes and has said he is not planning to allow his party members to vote with their conscience, on Saturday said his party would consider the proposals put forward by the government.
His finance spokesman John McDonnell told the BBC on Sunday the decision should not be made on a party-political lines.
"I am hoping that we can act as one, put aside party differences and look at the long term interests of the country," said McDonnell, who has previously called for Labour lawmakers to be allowed to vote in favor of strikes if they wished.
(Editing by Raissa Kasolowsky)