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Thousands have taken to Twitter to condemn the killing of innocent civilians in Syria after France launched wide-ranging air raids in the country in retaliation to Friday's .

The deadliest attack on French soil for many years saw militants from the so-called Islamic State group, kill at least 129 people in multiple attacks and leave more than 300 others wounded.

French President Francois Hollande promised a "merciless" response to the attacks.

"It is critical that the French government, as well as everyone else, doesn't react in exactly a way Islamic State wants us to react," Charlie Winter, a security analyst, told Sky News on Sunday.

But France staged pre-dawn raids on dozens of suspected Islamists anyway, and bombed Islamic State's stronghold in Syria, as the prime minister steeled the nation on Monday for more bloodshed.

French jets reportedly hit an IS command post, a recruitment centre, a munitions depot and a "terrorist" training camp in Raqqa late on Sunday, the defence ministry said.

The operation, coordinated with US forces, used a dozen aircraft which took off from Jordan and the United Arab Emirates.

The response was lambasted by thousands on social media using the hashtag .

Some emphasised the effects the attacks will have on civilians in Syria, as others posted harrowing images of children injured.

Many questioned whether the air raids were the best response, and the likelihood of causing further despair and anti-Western resentment among those living under the rule of the Islamic State group.  

Others, meanwhile, criticised the world's silence over the ongoing violations in Syria, Lebanon and Iraq in comparison with the outcry caused by Friday's attack in Paris: