David Cameron has promised a "comprehensive strategy" to win MPs' backing for bombing Islamic State militants in Syria as well as Iraq.
The prime minister told the Commons the Paris attacks had strengthened the case for air strikes, suggesting there could be a fresh vote on the issue.
He wanted to "do the right thing for our country", and hit the "head of the snake" of IS in Raqqa, Syria, he said.
MPs rejected strikes against Syrian government forces in a 2013 vote.
Labour leader Jeremy Corbyn said any military response should have the support of the international community and legality from the United Nations.
Two years ago, MPs voted against possible UK military action against President Bashar al-Assad's government in Syria.
Parliament later approved British participation in air strikes against Islamic State extremists in Iraq, which have been ongoing ever since.
Mr Cameron has promised British air strikes against IS will not be extended to Syria without Parliament's consent - and said he would only hold another vote when he was sure of a "consensus" among MPs.
In other recent developments:
- Mr Cameron, Prince William, London Mayor Boris Johnson and Labour leader Jeremy Corbyn are among the crowd at the England-France football match at Wembley Stadium, where supporters on both sides sang the French anthem "La Marseillaise"
- Chancellor George Osborne announced a doubling of funds to fight cybercrime to £1.9bn over five years, warning of the threat of Islamic State cyber-attacks
- RAF Tornados attacked a group of more than 30 IS fighters in Iraq on Monday, the MoD said
- Mr Corbyn said he supported "strictly necessary force" in the event of a terrorist attack following criticism of his opposition to a "shoot-to-kill" policy
- A number of senior Labour MPs, including former shadow chancellor Chris Leslie and shadow Europe minister Pat McFadden, spoke in the Commons about the need to give full support to the police and security services
- Police are investigating a deliberate fire at a mosque in Glasgow, and a petrol bomb attack on the home of a Muslim man in County Antrim
Downing Street has stressed it is not setting out a timetable publicly for a Commons vote yet, says BBC political correspondent Chris Mason.
An "important first step" would be setting out his case in a personal response to a recent Foreign Affairs Committee report, the prime minister said.
Sources indicated this would be done before the end of the month.
British planes had attacked 350 targets in Iraq and offered support to their allies' action over Syria, Mr Cameron said.
But he said Islamic State - also known as Isis, Isil or Daesh - did not recognise or respect the border between the two countries.
"It is in Syria, in Raqqa, that Isil has its headquarters and it is from Raqqa that some of the main threats against this country are planned and orchestrated," he said.
By BBC political editor Laura Keunssberg
David Cameron is pushing this right back up the agenda after months where the parliamentary arithmetic was not certain enough for him to risk a humiliating defeat.
It still is not.
The anti-action position of the Labour leadership makes another vote far from a forgone conclusion.
Mr Cameron said: "Raqqa, if you like, is the head of the snake. Over Syria we are supporting our allies - the US, France, Jordan and the Gulf countries - with intelligence, with surveillance and with refuelling.
"We face a direct and growing threat to our country and we need to deal with it not just in Iraq but in Syria too."
He said Britain could not protect its people "by sitting back and wishing things were different", or letting other countries "carry the burden".
Mr Cameron's speech came after IS said it was behind Friday's attacks in which 129 people were killed in bars, restaurants, a concert hall and at a stadium in Paris. The victims included Briton Nick Alexander from Essex.
David Cameron told the Commons he would be setting out a "full spectrum" approach, to include military action, counter-terrorism, humanitarian support and strategies for "defeating the poisonous narrative of extremism".
Responding to the prime minister's statement, Labour leader Jeremy Corbyn warned any response should not feed a cycle of violence and hatred.
He said he welcomed Mr Cameron comments at the G20 summit on Monday that "it's perfectly right to say a few bombs and missiles won't transform the situation", and a "whole plan" was needed.
BBC assistant political editor Norman Smith said many Labour MPs were unhappy with Mr Corbyn's indication that he would oppose almost any military intervention.
Downing Street could be hoping to capitalise on disarray in Labour circles over the issue and win opposition MPs' support, he added.
Labour MP Mike Gapes, a former chairman of the Foreign Affairs Committee, said it was illogical not to attack IS in Syria.
"It's like in World War Two, bombing Hamburg, but not attacking Berlin," he said.
However, there was opposition from some MPs. Alex Salmond, the SNP's foreign affairs spokesman, said a UN mandate would be a condition for his party's support in any vote.
Liberal Democrat leader Tim Farron warned against being dragged into another Iraq-style war, saying that any action needed to be effective rather than "knee-jerk".