Syria war

Under the plan, rebel-held eastern Aleppo would remain under opposition control if rebel fighters withdrew.

Foreign Minister Walid al-Muallem, who met the UN envoy to Syria on Sunday, called the idea a violation of "national sovereignty".

Earlier, eight children died in government-held western Aleppo after rebels hit a school, state media say.

In a rebel-held area, a barrel bomb killed a family of six, activists say.

Local medics say the victims in the al-Sakhour district suffocated to death because the bomb was laced with chlorine gas.

Defence Minister Sergei Shoigu said the bombing had been halted early on Tuesday.

Russia had already announced an eight-hour pause between 08:00 (05:00 GMT) and 16:00 on Thursday.

Mr Shoigu urged rebels and civilians in the besieged eastern area of the city to use humanitarian corridors to leave.

Russian warplanes pounded the rebel-held areas of Aleppo shortly before announcing Tuesday's suspension, activists say.

The Syrian army says it is implementing the truce, which began at sunset, but rebel groups have been more guarded.

US Secretary of State John Kerry, who helped broker the deal, warned it could be the last chance for peace in a united Syria.

Humanitarian groups are hoping to make aid deliveries to the worst-hit areas, especially the war-torn city of Aleppo.

Mr Kerry, speaking at the state department in Washington, said early reports indicated "some reduction in violence".

Clashes in places where so-called Islamic State (IS) was not present were a "source of deep concern", the US envoy to the anti-IS coalition tweeted.

Turkish forces have attacked what they say are Kurdish "terrorists" since crossing the border last week.

But the Kurdish YPG militia says Turkey just wants to occupy Syrian territory.

Turkish authorities said the dead, killed in shelling and air strikes on Sunday, were all Kurdish militants.

Separately, a monitoring group said at least 35 civilians and four militants were killed by Turkish strikes in villages near Jarablus on Sunday.

It is not yet clear whether the two reports were referring to the same incident.

The strikes came on the fifth day of a Turkish military operation to target so-called Islamic State (IS) militants and Kurdish militia inside Syria, dubbed Operation Euphrates Sword.

The Mi-8 transporter came down in Idlib province. It was carrying three crew and two officers, Russia's defence ministry said.

The helicopter was returning from delivering humanitarian aid to the besieged city of Aleppo, it said.

It is not clear which group brought the helicopter down.

An alliance of rebel groups, including hardline jihadist factions, is the dominant power in Idlib.

Russia has previously, though seldom, lost aircraft since it launched operations in support of the Syrian government at the end of September 2015.