BEIRUT/PARIS/LONDON (Reuters) - The Syrian opposition said on Friday the government was mobilizing forces on many fronts despite an agreement to cease hostilities, and cast doubt on whether peace talks planned for next week would take place.

Protesters carry Free Syrian Army flags while riding pick-up trucks during an anti-government protest in the town of Marat Numan in Idlib province, Syria March 4, 2016. REUTERS/Khalil Ashawi

As rockets fired by government forces were reported to hit near the rebel-held town of Jisr al-Shughour in Idlib province, an influential rebel group said there could be no ceasefire while attacks continue.

An unprecedented U.S.-Russian agreement that came into effect on Saturday has slowed the pace of the 5-year-old war, but rebels fighting President Bashar al-Assad say the government has kept up attacks on strategically important frontlines.

The opposition has yet to say whether it will attend peace talks planned for March 9. Opposition coordinator Riad Hijab said the conditions for talks were “not favorable” but it was too early to say whether they would happen or not.

Assad, his war effort buoyed by five months of Russian air strikes, has said the army is respecting the agreement. The truce does not cover the al Qaeda-linked Nusra Front or Islamic State, two groups which Moscow and Damascus have said they will continue to fight.

The Nusra Front is widely deployed across western Syria in close proximity to groups that agreed to cease fire, many of which say they believe the government and its Russian allies can use the presence of the militants as an excuse to fight on. Syrian state media have said very little about operations in western Syria since Saturday.

The Syrian opposition appears at odds with its Western backers over the success of the truce so far.

European leaders told Russian President Vladimir Putin they welcomed the fact the fragile truce appeared to be holding, and it should be used to try to secure peace without Assad.

But Hijab said government forces had attacked more than 50 opposition-held areas where groups that approved the truce were based.

Mohamad Alloush, a senior official in one of the largest rebel groups, Jaish al-Islam, told Reuters the government was mobilizing forces to “occupy very important strategic areas”. His group, in a separate statement, said the war had not stopped as far as it was concerned, and that a ceasefire was not possible while “militias and states kill our people”.

The head of another rebel group, who asked not to be identified for security reasons, said 40 army vehicles loaded with weaponry were seen heading northwards on Thursday night.

Government operations were “focused on Homs, on the coast mostly”, while Aleppo - the target of a major government offensive a month ago - was relatively calm, he said.

The Syrian Observatory for Human Rights, a Britain-based organization that tracks the conflict, said heavy shelling and rocket fire landed around the town of Ghasaniya near rebel-held Jisr al-Shughour on Friday.

It also said warplanes on Friday mounted the first air strike against the rebel-held town of Douma near Damascus since the start of the cessation. It did not say whether the planes were Russian or belonged to the Syrian army.

“THE WAR HAS NOT STOPPED”

The U.S. and Russian sponsored cessation of hostilities agreement, which has not been signed directly by the Syrian warring parties and is less binding than a formal ceasefire, is the first of its kind during a conflict that has killed more than 250,000 people.

U.N. Syria envoy Staffan de Mistura said on Thursday the agreement was holding but remained fragile and incidents had been contained. The U.S. State Department said on Thursday there had been no significant violations in the preceding 24 hours.

Assad said earlier this week that the militants had breached the deal from the first day and the army was refraining from responding to give the deal a chance.

Much of southern Syria, including areas near the border with Jordan, has been calm, though a rebel spokesman said government forces were also mobilizing there. “If the truce ends, the regime is ready to attack in a number of areas,” said Abu Ghiath al-Shami of the Alwiyat Seif al-Sham group.

The government, backed by Russian air power and fighters from Iran and Lebanon’s Hezbollah, made significant territorial gains against rebels since the new year, focused in areas of western Syria near the borders with Turkey and Jordan.

De Mistura attempted to hold peace talks a month ago but these failed before they had even started in earnest.

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France, Britain and Germany called on the opposition to attend the talks, but warned that the negotiations would succeed only if humanitarian access were granted and the truce respected.

“If these two conditions are not met, then the negotiation process is bound to fail, which we do not want,” French Foreign Minister Jean-Marc Ayrault told journalists in Paris.

RUSSIA SAYS COMMITTED TO CEASEFIRE

The opposition council, known as the High Negotiations Committee, has said humanitarian demands previously listed as conditions for peace talks have still not been met. These include free access for humanitarian aid to opposition-held areas blockaded by government forces and a release of detainees.

Alloush, the senior Jaish al-Islam official, told Reuters aid delivered in recent days to opposition-held areas “is not enough to meet 10 percent of the needs, and nothing has entered most of the areas”.

In a conference call between the leaders of Germany, France, Britain, Italy and Russia, Putin confirmed Russia’s commitment to the ceasefire, German Chancellor Angela Merkel said.

Western countries want Assad to leave power, and the main opposition council says he should leave before any political transition starts. Russia has stood by him, while saying only Syrians should decide his fate.

In an interview with France 24, U.N. envoy de Mistura also said it was up to Syrians to decide: “Why should we be saying in advance what should the Syrians say, as long as they have the freedom and the opportunity of saying so?”

A spokeswoman for British Prime Minister David Cameron said the European leaders told Putin the truce must be used to try to secure peace without Assad, but their main point on the phone call was to welcome the fact the truce appeared to be holding.

The Kremlin said the leaders agreed that the cessation of hostilities had started yielding its first positive results.

“The importance of continued uncompromising fight against Islamic State, the Nusra Front and other terrorist groups” was stressed during the conversation, it said.

Hijab reiterated opposition complaints that the United States had made many concessions to Russia, including on the cessation of hostilities agreement.

“This is unfortunately at the expense of the Syrian revolution,” he said.