DAMASCUS - Former Syrian prime minister turned key opposition leader Riad Hijab has told AFP in an interview the forces fighting the regime need "actions, not words" from countries that support them.

He said the opposition urgently required surface-to-air missiles to counter the air strikes carried out by the regime and their Russian allies.

And he called for tougher action against President Bashar al-Assad, who he claimed had effectively received a "green light" from Moscow and Washington to continue bombing civilian areas.

"What we want are practical and effective measures on the ground. We don't need statements or pretty words in the media because that doesn't produce any results," Hijab told AFP.

Hijab, who was speaking in Paris on Wednesday after attending a meeting of Arab and European allies of the Syrian opposition as well as US Secretary of State John Kerry, said he was frustrated at the lack of tough action against the Damascus regime.

He accused the regime of responsibility for "more than 2,300 violations of the ceasefire" since it came into effect on February 27.

Hijab accused the Syrian regime and their Russian allies of committing war crimes.

"In April alone, there were 27 massacres, with bombings of markets, schools and hospitals carried out by the regime. We saw what happened in Aleppo recently," he said.

The ceasefire between regime forces and non-jihadist rebels in Syria, overseen by Moscow and Washington, was shattered at the end of April, most strikingly in Aleppo, the strategic city in northern Syria whose control is split between government and rebel forces.

Around 300 people were killed in a surge in fighting in the city.

- 'Green light to Assad' -

A fragile new ceasefire was introduced last week and Russia and the United States agreed to "redouble" efforts to find a political solution to a war that has lasted five years and cost the lives of 270,000 people.

"It's completely insufficient," Hijab said. "The joint statement by the Russians and the Americans says they want to 'minimise' the bombing of civilians and civilian areas as much as possible.

"That is like giving the regime a green light to continue its abuses and saying: 'You are killing 100 Syrians a day. Well today you mustn't kill more than 10."

The regime defends its air strikes by saying it is targeting "terrorist groups", meaning the Al-Nusra Front (the Syrian branch of Al-Qaeda) and the Islamic State group, neither of which are included in the ceasefire.

"The Syrian people have been dying for five years. We want actions, not words, from our friends," Hijab said.

"We hope that the United States, the French, the British, the Germans and others are going to act on the ground," Hijab said.

The opposition forces' main plea, as it has been since the start of the war in 2011, is for weapons.

"The United States has prevented us obtaining anti-aircraft weapons for five years. And until recently they were blocking us from getting anti-tank weapons," he said.

"We are fighting on several fronts: against Daesh (the Arab acronym for Islamic State), there have been fierce battles in recent days around Aleppo, Homs and Damascus and in the south.

"We are fighting against regime forces, against the (Kurdish) PYD, against religious militia from Iraq and Lebanon, and against Afghan mercenaries and others... We need weapons that can make a difference on the ground."

Hijab also called for the 17-nation International Syria Support Group (ISSG), which is due to meet in Vienna next Tuesday, to take measures to force the regime to respect the international community's humanitarian demands.

The ceasefire, he said, "is not an end in itself".

"The solution for Syria is a genuine political transition," said the man who oversees the opposition's negotiations in Geneva.

Three rounds of UN-backed peace talks since the start of the year have failed to make significant progress. The most recent round, in April, was suspended when fighting resumed in Aleppo.

"We want to return to Geneva," Hijab said. "We're at an impasse at the moment because the regime does not want to talk about a (political) transition."

He stressed though that the opposition's approach remained unchanged -- there can be no solution that includes Assad.

"It is completely unrealistic to imagine that he can stay in power," said Hijab, who was serving as prime minister under Assad when he fled Syria with his family in August 2012 to join the opposition.