David Cameron has said he will call a one-day Commons debate and vote on Wednesday over UK air strikes against so-called Islamic State in Syria.
The decision comes after Labour leader Jeremy Corbyn said he would grant his MPs a free vote on the matter.
The prime minister said there was “growing” parliamentary support for air strikes, saying it was “the right thing to do” and in the national interest.
Mr Corbyn criticised the decision not to hold a two-day debate on the issue.
The Labour leader said it showed Mr Cameron’s case for air strikes in Syria “is falling apart” and said the prime minister should “stop the rush to war”.
Prior to Mr Cameron’s statement, Mr Corbyn called for two days’ of debate ahead of any vote, saying a single day “would inevitably lead to important contributions being curtailed”.
Responding to those calls, Mr Cameron – who was speaking in Downing Street shortly after returning from the Paris climate summit – said there would a “very long and full” debate.
“We will take the action necessary to make sure we have, in many ways, the equivalent number of questions we would often have across a two day debate in one day,” he said.
“I want MPs to be able to have full consideration, to make speeches, to make points, to ask me questions, to examine the government’s case,” he added.
Announcing his decision, Mr Cameron said he would recommend to his cabinet on Tuesday “that we hold a debate and a vote in the House of Commons to extend the air strikes that we have carried out against Isil in Iraq to Syria, that we answer the call from our allies and work with them, because Isil is a threat to our country and this is the right thing to do.”
The prime minister has previously said he would not call a debate and vote on extending UK air strikes from Iraq to Syria unless he was confident he could win it.
Asked if he felt he now had the numbers in the Commons, he said: “I believe there’s growing support across parliament for the compelling case there is to answer the call from our allies to act against Isil in Syria and in Iraq.”
Mr Cameron said the Islamic State group – also referred to as IS, Isil or Daesh – was a threat to the UK’s security, and reiterated his case for extending UK air strikes to Syria.
“The headquarters in many ways of the terrorists actually is in Syria – and it makes no sense to recognise this border in the action we take when Isil themselves don’t recognise this border.
“So it’s in the national interests, it’s the right thing to do. We’ll be acting with our allies, we’ll be careful and responsible as we do so. But in my view it’s right to do this to help keep our country safe.”
Mr Cameron said RAF strikes against IS targets in Iraq – action authorised by MPs in September 2014 – had been “successful”.
“It’s shrunk Isil territory by 30%, it’s damaged their infrastructure, it’s set them back – it’s right to extend that action to Syria,” he said.
The prime minister stressed that military action would be part of “a broader strategy” that included political, diplomatic and humanitarian efforts.
He acknowledged that the strategy would “take time”.
But he said it was right to go after terrorists “who threaten people in our country just as they attacked and killed those people on the streets of Paris, the streets of Ankara and the streets of Beirut, and indeed British people on the beaches of Tunisia”.
A spokesman for Mr Corbyn said: “By refusing a full two-day debate, David Cameron is demonstrating he knows the debate is running away from him, and that the case he made last week is falling apart.
“The prime minister should stop the rush to war to allow for a full discussion of the issues in parliament.
“Matters of national security are far too important to be bulldozed through the House of Commons for political convenience.”
In order to win the vote, Mr Cameron will need enough Labour MPs to back military intervention to make up for Conservative MPs who oppose the action.
The UK Parliament’s third largest party – the SNP – opposes bombing IS in Syria.
After a meeting of Labour’s shadow cabinet on Monday afternoon to discuss the party’s position on air strikes, it was announced that Labour MPs would be given a free vote.
Leader Jeremy Corbyn is opposed to military intervention in Syria, but some in his shadow cabinet and the parliamentary Labour Party support the government’s case.
A spokesman for Mr Corbyn said the shadow cabinet had “accepted his recommendation” of a free vote.
Foreign Secretary Philip Hammond has said he is “confident” that there will be “a majority of parliamentarians” in favour of air strikes against IS in Syria.