Protesters in UK and Spain demand their governments not launch air strikes against ISIL in Syria after Paris attacks.

Thousands of people demonstrated in London and Madrid against the potential participation of their countries in air strikes in Syria, as political momentum grows to broaden the fight against the Islamic State of Iraq and the Levant (ISIL).

At least 5,000 people gathered in central London on Saturday carrying placards reading “Don’t bomb Syria”, “Drop Cameron, not bombs”, and “Don’t add fuel to the fire.”

“[Prime Minister] David Cameron’s incoherent proposals for action in Syria will do nothing to weaken ISIL, but will instead inflame the civil war, deepen the misery of the Syrian people, and increase the terrorist risk,” said the Stop the War Coalition protest movement.

Cameron on Thursday laid out the case for British fighter jets, already bombing ISIL targets in Iraq, to join France, the US, and others in targeting ISIL strongholds in neighbouring Syria.

A parliamentary vote on bombing Syria is expected as early as this week, and many formerly reluctant politicians are thought to have changed their minds after the Paris attacks earlier this month.

Spanish Prime Minister Mariano Rajoy, who faces a December general election, said he would hold off on any decision on action in Syria [JJ Guillen/EPA]

Also on Saturday, about 5,000 people demonstrated against potential Spanish involvement in the conflict, with protesters chanting “No to war” outside the Reina Sofia museum in the capital Madrid.

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Protesters answered a “not in our name” petition from dozens of artists that received about 34,000 online signatures to date, as European governments consider joining the air war in Syria.

Prime Minister Mariano Rajoy, who faces a December general election, said he would hold off on any decision.

“Decisions have to be well thought through, as in any aspect of life,” said Rajoy, who added Madrid was in touch with its allies pending a clear plan of action.

Rajoy’s Popular Party is mindful of how in March 2004, under his predecessor Jose Maria Aznar, who had backed the US intervention in Iraq a year earlier, lost the general election which took place three days after 191 people were killed in a series of Madrid train bombings.