Syrian regime air strikes on the Islamic State group stronghold Raqa have killed at least 95 people, while a delegation from President Bashar al-Assad's government held talks Wednesday with key ally Russia.

The bombing Tuesday was the deadliest by Assad's air force in Raqa since fighters from the Sunni extremist IS seized 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.

It was unknown how many jihadists were killed.

Raqa was the first and only provincial capital lost by the regime, and was later overrun by IS, which has used it as the headquarters for 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 stepped up air strikes against IS-held towns in the north and east in recent months, 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 the jihadists.

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 coalition strikes" against the jihadists.

- Behind closed doors -

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 in Sochi Wednesday.

But the content of the closed-door discussions was not revealed.

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

Two rounds of UN-brokered talks were held in Switzerland in early 2013. Both ended without agreement.

After Wednesday's meeting, Russian news reports quoted Foreign Minister Sergei Lavrov as saying no new talks were possible at this time.

"If you think that a conference will be announced similar to the one that was held in... January this year with the participation of 50-odd states, thousands of journalists, bright lights, there won't be such a conference," Interfax quoted him as saying.

Lavrov blamed "external interference in the Syrian conflict" for undermining the prospects for new direct negotiations.

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

The coalition, which has been internationally recognised but lacks influence in Syria, has voiced scepticism about prospects for progress.

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

In September, Putin said their delivery 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.

After the meeting, Lavrov was quoted as saying "Russia will continue helping Syria protect itself against terrorism," without elaborating.

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

- 'Most brutal threat' -

German Chancellor Angela Merkel described IS Wednesday 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.

In Iraq, pro-government forces have recaptured some of the territory lost to IS, 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 its warplanes had carried out 10 air strikes against IS fighters in Syria since Monday, while the wider coalition waged seven strikes against the group in Iraq.

Iraqi security forces and allied tribesmen were battling Wednesday to defend the governor's office in Anbar provincial capital Ramadi from an attack by the IS fighters, officers said.

And Kurdish peshmerga forces held off a major IS attack in the oil-rich province of Kirkuk, other officers said.

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