BEIRUT (Reuters) – Russian warplanes bombed Syrian rebel-held areas in northwestern Syria and government forces pounded a suburb of the capital on Thursday, ahead of a planned halt to fighting which rebels predicted Damascus and Moscow would ignore.

The “cessation of hostilities” agreed by the United States and Russia is due to take hold on Saturday morning from midnight. But opponents of President Bashar al-Assad say they expect the government to press on with its advance, by branding opposition fighters al Qaeda militants unprotected by the truce.

Damascus has agreed to the deal, as has the main opposition alliance, though it is only ready to commit for two weeks given its deep reservations. But the government and its allies will be permitted to forge on with strikes against jihadist militants of Islamic State and an al Qaeda-linked group, the Nusra Front.

The government also says the agreement could fail if foreign states supply rebels with weapons or insurgents use the truce to rearm.

Fighting in the final days before the truce has focused on Daraya, a besieged suburb of the capital held by fighters the government describes as Nusra militants but rebels say are from other groups, and on the northwest near the Turkish frontier.

Four months of Russian air strikes turned momentum Assad’s way in a 5-year-old war that has killed more than 250,000 people, created the world’s worst refugee crisis and seen Islamic State fighters declare a “caliphate” in Syria and Iraq.

The multi-sided civil war has drawn in most regional and global powers, with Western countries, Arab states and Turkey forming a coalition against Islamic State while also backing rebels fighting to overthrow Assad. Russia and Iran support him.

BARREL BOMBS

The Syrian Observatory for Human Rights, a British-based group that monitors the conflict, said army helicopters dropped at least 30 “barrel bombs” on Daraya on Thursday. Assad’s opponents say the army drops oil drums filled with explosives and shrapnel to cause indiscriminate harm in rebel areas.

The government blamed groups linked to Nusra for firing mortars into residential areas of Damascus, killing at least one person.

A spokesman for rebels in southern Syria predicted Daraya would be the first place where the truce would collapse.

“They want to exploit the ceasefire and focus their fire on Daraya to take it. This will be the first breach. We won’t accept it,” said Abu Ghiath al-Shami, spokesman for the Alwiyat Seif al-Sham group, part of a rebel alliance in the south.

A Syrian military source also signaled that Damascus would not cease fighting in Daraya.

“There is evidence that the ones there are Nusra Front. They found documents, books, flags that point to the Nusra Front being in Daraya,” the military source said. “In any place where there is Nusra Front, we will continue operations.”

Fighting has also escalated in the last two days in the northwestern province of Latakia, where Free Syrian Army groups backed by Assad’s foreign enemies operate close to Nusra fighters and other jihadists.

“The regime wants to try to retake all of northern Latakia before Feb. 26,” said Fadi Ahmad, spokesman for the First Coastal Division rebel group, speaking to Reuters from the area.

VERY FIERCE BATTLES

“The battles are very fierce. Yesterday, there were heavy battles in the part of rural Latakia that is still with us,” he said, adding he did not expect the government or its Russian allies to abide by the truce: “Three minutes ago I saw a Russian plane in the sky hitting us here in rural Latakia.”

The Syrian military source also said operations were taking place in the northern Latakia area.

Recapturing areas of Latakia province at the Turkish border has been a top priority for Damascus and its allies since Russia began its strikes. It is one of several areas where the government has made major gains this year.

Rami Abdulrahman, director of the Observatory, confirmed heavy air strikes in northern Latakia on Wednesday and Thursday.

He predicted the presence of the Nusra Front and like-minded groups would give the government grounds to press on with fighting there under the agreement.

One of the main purposes of the cessation of hostilities is to allow aid to reach civilians, especially in besieged areas cut off from supplies.

A U.N. air-drop of food to 200,000 people in the besieged city of Deir al-Zor failed on Wednesday, with all 21 palettes dropped by parachute either damaged, landing in no-man’s land or unaccounted for, a U.N. World Food Programme spokeswoman said.

U.N. advisor Jan Egeland nevertheless said the cessation of hostilities could rescue the civilian population from “the abyss” and end the “black chapter” of sieges.

Assad told Russian President Vladimir Putin on Wednesday his government was ready to help implement the halt to fighting. The two leaders nevertheless stressed the importance of an “uncompromising” fight against Islamic State, the Nusra Front and other jihadists not party to the truce.

U.S. President Barack Obama on Wednesday said he was cautious about raising expectations, but if some progress were made that would lead to a political process to end the war.

“THERE’S NO PLAN B”

Russian officials have seized on comments by Secretary of State John Kerry that Washington would consider a “Plan B” if the ceasefire failed. Russia’s RIA news agency quoted Foreign Minister Sergei Lavrov saying there was no such “Plan B”.

Foreign Ministry spokeswoman Maria Zakharova accused “some U.S. officials” of trying to “sabotage” the ceasefire plan.

However, after more than five years of failure to negotiate any end to fighting, and with Russia’s intervention having had a decisive impact on the ground, it was not clear what sort of fallback plan Washington might consider if the truce fails.

Bob Corker, chairman of the U.S. Senate Foreign Relations Committee and a Republican critic of the Obama administration, said of Putin: “I think he understands there’s no ‘plan B’.”

The Russians were “now dominating,” Corker told MSNBC. “It’s totally in Russia’s hands now.”

United Nations Syria envoy Staffan de Mistura said he would announce on Friday a date for a new round of talks between Syria’s warring parties. The last talks were called off this month before they got under way, with rebels saying they could not talk while government troops advanced and Russia bombed.

The Syrian Kurdish YPG militia told Reuters on Wednesday it would abide by the plan to halt fighting but reserved the right to respond if attacked. The YPG is an important partner in the U.S-led coalition fighting Islamic State, but has also been fighting other insurgent groups in northwestern Syria near Aleppo, and is considered an enemy by NATO member Turkey.

Turkey, which has fired across the frontier at the YPG, said it would not consider itself bound by the cessation of hostilities if it were threatened by either the YPG or Islamic State.

(Additional reporting by Jack Stubbs in Moscow, Tom Miles in Geneva and Susan Heavey in Washington, writing by Tom Perry and Peter Graff, editing by Peter Millership)