ALEPPO, Syria (AFP) - Displaced families returned home and schools reopened in rebel-held districts of Syria's Aleppo on Saturday (May 7) after a truce was extended for 72 hours in the battleground northern city.

More than 300 civilians were killed in two weeks of fighting in the divided city before the truce took hold on Thursday, with regime air strikes on the opposition-held east and rebel shelling of its regime-controlled west.

Residents trickled back into eastern areas of Aleppo, encouraged by a halt in the deadly violence, an AFP reporter said.

"I decided to come home after relatives told me it was calm," father-of-six Abu Mohammed said.

"We left because it was carnage here. The air strikes were incredible," said the resident of the rebel-held Kalasseh district.

The international community hopes that a drop in fighting can revive faltering peace talks to end a five-year war that has killed more than 270,000 people and displaced millions.

Schools in Aleppo's east reopened Saturday after staying closed for more than two weeks.

"There were many bombings so our parents got scared and stopped sending us to school," one schoolboy told AFP.

A monitor reported rebel shelling of areas in western Aleppo but said there were no casualties.

Russia's defence ministry said the truce had been extended "in order to prevent the situation from worsening" just minutes before an initial 48-hour truce was due to expire.

"The regime of silence in the province of Latakia and in the city of Aleppo has been extended from 00:01 (local time) on May 7 (2101 GMT Friday) for 72 hours," a ministry statement said.

Violence in Aleppo last month severely threatened a nationwide ceasefire between President Bashar al-Assad's regime and non-jihadist rebels.

Washington has been working with Moscow to pressure the regime to stop the violence and revive the February 27 truce.

"While we welcome this recent extension, our goal is to get to a point where we no longer have to count the hours and that the cessation of hostilities is fully respected across Syria," US State Department spokesman John Kirby said.

But fighting raged elsewhere, said the Britain-based Syrian Observatory for Human Rights said.

Apparent US-led air raids overnight on Islamic State in Iraq and Syria (ISIS) group strongholds in northern Aleppo killed six people, including women and children, as well as four ISIS leaders, it said.

In the central city of Hama, a raid by Syrian security forces on a prison failed to end a mutiny involving around 800 mostly political detainees sparked by an attempt to transfer inmates to another jail near Damascus where executions have been reported.

The head of Syria's main opposition group, Riad Hijab, on Saturday called for "intervention from the UN Security Council to guarantee the safety of detainees in the Hama prison".

ISIS and regime forces clashed near the divided eastern city of Deir Ezzor on Friday, the Observatory said, adding that five jihadists and 10 pro-regime fighters were killed.

Thirteen Iranian Revolutionary Guards advisers have been killed in Syria in recent days and 21 wounded, Iranian media reported on Saturday.

The deaths and injuries occurred in Khan Tuman village southwest of Aleppo which was overrun this week by Al-Nusra front, Al-Qaeda's Syria affiliate.

Syrian troops and allied forces have been battling the jihadists to recapture the village, the Observatory said, adding that since Thursday night 119 fighters have been killed there.

Iranian deputy foreign minister Hossein Amir Abdollahian late Saturday called Khan Tuman's capture a breach of the ceasefire that proves "terrorists and irresponsible armed groups called moderates... have no belief in a political solution".

An international outcry has grown over air strikes Thursday on a camp for the displaced near the closed Turkish border that killed at least 28 people including women and children.

Anti-regime activists have blamed the regime, but the Syrian military has denied the accusation.

Russia suggested Syria's Al-Qaeda affiliate Al-Nusra Front could have shelled it, while the United States said that the circumstances are unclear.

In Madrid, meanwhile, the Spanish Press Federation (FAPE) announced late Saturday that three Spanish journalists kidnapped in Syria about 10 months ago had been freed.

FAPE's president Elsa Gonzalez told AFP the journalists were "in a safe place" and would be landing at an air base on the outskirts of Madrid on Sunday.

Antonio Pampliega, Jose Manuel Lopez and Angel Sastre had last been seen in July 2015 in Aleppo, where they were reporting on fighting.