The Syrian army said it would observe a 72-hour truce to mark the Islamic festival of Eid al-Fitr.

The "regime of silence" applies across the Syrian Arab Republic from 1am on 6 July to midnight on 8 July to coincide with the time of the celebrations at the end of month of fasting. President Assad's army announced the truce in a statement on Wednesday but did not say whether it extended to action against jihadist groups such as ISIS or al-Qaeda linked al-Nusra Front.

There was no indication in the announcement that the ceasefire had been discussed with oppents but a number of rebel groups said they would respect it.

Western-backed Free Syrian Army and other allied rebel factions said they would hold the truce "so long as the other side does the same".

Mohammed Alloush, the opposition's former chief peace negotiator, said in a statement on Twitter: "Until now, [the government] has not abided by what it has announced, in that it has launched a number of attacks in various areas today."

The US secretary of state John Kerry said he hoped the truce would be extended into a longer lasting peace deal.

"We very much welcome the Syrian army declaration of 72 hours of quiet," said Kerry at a news conference in Georgia.

"We are trying very hard to grow these current discussions into a longer lasting ... enforceable, accountable cessation of hostilities that could change the dynamics on the ground."

But despite the ceasefire announcement the Syrian Observatory for Human Rights, a British based monitoring group, said rebel held areas in Aleppo had come under fire on Wednesday. At least one civilian was killed and several wounded.

The Syrian President Bashar Al-Assad made an unusual public appearance and joined the Eid prayers at a mosque in Homs on Wednesday. Once under rebel control, the devastated town is now mainly government controlled with the rebels pushed into one besieged neighbourhood on the edge of the city.