Syrian regime air strikes on Islamic State group stronghold Raqa killed at least 95 people as a government delegation held talks with key ally Russia Wednesday on relaunching peace negotiations.

The bombing on Tuesday was the deadliest by President Bashar al-Assad's air force in Raqa since Sunni extremist IS fighters seized control of the city last year and declared it their capital.

More than half of the dead were civilians, according to the Syrian Observatory for Human Rights, which monitors the war through a network of sources.

It was unknown how many fighters were killed.

Raqa was the first provincial capital to fall from regime control, and it was later overrun by IS which has used it as the capital of its self-proclaimed "caliphate" straddling Syria and neighbouring Iraq.

The multi-sided Syrian conflict has killed more than 195,000 people and forced millions from their homes since it began three and a half years ago as an uprising against Assad's regime.

The government has in recent months stepped up its air strikes against IS-held towns in the north and east, with most of the casualties reported to have been civilians.

Raqa has also been the target of repeated air strikes by the US-led coalition fighting thefighters.

Syria's exiled opposition National Coalition condemned the strikes as a "brutal massacre", warning that "many seem now convinced that Assad is the major beneficiary of the US-led coalition strikes" against the jihadists.

Staunch Russian support

In Russia, a Syrian delegation headed by Foreign Minister Walid Muallem held talks with Assad's key ally President Vladimir Putin at his Black Sea retreat of Sochi on Wednesday.

No statement was issued after the meeting.

Ahead of the talks, Russia's foreign ministry said the issue of "mending the political process" would be high on the agenda.

Russian Foreign Minister Sergei Ryabkov said Moscow had "many questions concerning the prospects of a political settlement" to the Syrian conflict.

A second round of UN-brokered talks was held in Switzerland in early 2013 but ended without agreement.

A former leader of the National Coalition, Moaz al-Khatib, is reported to have held talks at the Russian foreign ministry on November 7.

But the Coalition, which has been internationally recognised but lacks influence in Syria, has voiced scepticism about prospects for progress.

It accuses Syria and Russia of trying to handpick an opposition with whom to negotiate.

"These attempts don't provide any kind of political path to a solution in Syria," Coalition secretary-general Naser al-Hariri told AFP.

"The representatives of the Syrian people are well-known and must be dealt with."

The delegation from Damascus was also expected to push for the delivery of long-sought S-300 anti-aircraft missiles.

Last September, Putin said delivery of the S-300 missiles had been suspended without saying why, though the decision came after Israeli Prime Minister Benjamin Netanyahu visited Russia to ask Moscow to halt the shipments.

The UN and human rights groups have repeatedly called on all sides in the war, including the Assad regime, to stop using weapons that fail to discriminate between civilians and military targets.

Scenes of carnage

Amateur video footage distributed by activists in Raqa showed several bloodied bodies laid out on a street near an apparent bombing site, as an ambulance rushed to the scene.

Aid workers in red overalls bearing the Red Crescent symbol could be seen placing the corpses into white body bags.

Raqa was the first and only provincial capital to fall from Syrian government control, but shortly after it was captured by rebels, IS fighters seized the city.

They have used it as the de facto capital of their so-called "caliphate" in the territory they control in Syria and Iraq.

German Chancellor Angela Merkel on Wednesday described IS as "one of the most brutal threats to the lives of the people in the region... that there has ever been".

"Their radical lack of inhibition and willingness to murder also threatens our security," she said, voicing concern about foreigners going to fight in Syria and Iraq.

Pro-government forces in Iraq have recaptured some of the territory lost to the fighters, but the militants still hold large areas of the country including the cities of Mosul, Tikrit and Fallujah.

France, part of the coalition fighting IS in Iraq, said six Mirage fighter jets would be deployed on Thursday to Jordan to assist in the strikes across the border.

The US military said Wednesday that its warplanes had carried out 10 airstrikes against IS fighters in Syria since Monday while the wider coalition waged seven strikes against the group in Iraq.