British Prime Minister David Cameron urged skeptical lawmakers to back airstrikes on the Islamic State group in Syria, saying Thursday that the Paris attacks have given the fight new urgency and Britain owes it to key allies to act.
Cameron told the House of Commons that President Barack Obama and French President Francois Hollande had urged Britain to join the military campaign in Syria.
"These are our closest allies and they want our help," he said.
"We have to hit these terrorists in their heartlands. We have not and we must not shirk our responsibility for security or hand it to others."
Some previously skeptical lawmakers said they were convinced, but Cameron has not yet announced a date for a House of Commons vote on airstrikes.
The Royal Air Force is part of a U.S.-led coalition attacking IS militants in Iraq, but not in Syria. Cameron has been reluctant to seek backing for strikes in Syria since lawmakers voted down his 2013 plan to launch RAF strikes against the forces of Syrian President Bashar Assad.
Many Britons are wary of getting drawn in to another Middle Eastern conflict after messy, bloody wars in Iraq and Libya.
Earlier this month, Parliament's Foreign Affairs Select Committee said British airstrikes would be "incoherent" and ineffective without a plan to end Syria's four-year civil war.
Cameron replied Thursday with a 36-page letter, arguing that Britain should act to deny the Islamic State group a "safe haven" from which to plot mass-casualty attacks like the Nov. 13 rampage that left 130 dead and hundreds wounded in Paris.
He said airstrikes should be part of a "comprehensive overall strategy" to destroy IS, end the Syrian war and help rebuild the country.
Attempting to allay legislators' concerns, Cameron answered questions for more than two hours in the House of Commons.
He argued that military action was legal under the U.N. charter's right to self-defense. And he said while ground forces would also be needed, they would not be British.
Cameron said airstrikes would not increase the already-high risk of an attack in Britain. He said British authorities have foiled seven attacks in the past year either planned or inspired by IS.
Cameron said he would only seek a vote in Parliament if "there is a clear majority for action," so as not to hand IS "a publicity coup."
The main opposition Labour Party remains divided. Leader Jeremy Corbyn, whose left-wing views are at odds with some of his lawmakers, said military action could have "unintended consequences" — as it did in Iraq, Libya and Afghanistan. He wrote Thursday to Labour legislators to say he wouldn't back airstrikes because Cameron had not set out "a coherent strategy" to defeat IS.
Labour's leadership in Parliament met Thursday, but didn't decide whether to allow the party's lawmakers a free vote. Another meeting is scheduled for Monday.
The Scottish National Party's Angus Robertson said his legislators would not support airstrikes without effective ground support and "a fully costed reconstruction and stability plan."
The debate is shadowed by the legacy of Parliament's divisive 2003 decision to join the U.S.-led invasion of Iraq. That decision was made on the basis of flawed intelligence about Iraqi leader Saddam Hussein's alleged weapons of mass destruction, and without an adequate plan for postwar reconstruction.
"This is about learning the lessons of Iraq," Cameron said, adding that — unlike in Iraq — "we are not taking or proposing to take military action to achieve regime change in Syria."
