ALEPPO, Syria – Russia on Monday announced an eight-hour "humanitarian" ceasefire in Aleppo later this week, as the EU warned that the Syrian regime’s Moscow-backed assault on the city could amount to war crimes.

The United Nations and European Union welcomed the announcement, but said Thursday’s planned pause in fighting needed to be longer to allow the delivery of humanitarian aid.

Meanwhile, dozens of civilians including 12 members of the same family were killed in heavy bombardment of rebel-held eastern sectors of the embattled city Monday, a monitoring group said.

"We have taken a decision not to waste time and to introduce ’humanitarian pauses’, mainly for the free passage of civilians, evacuation of the sick and wounded and withdrawal of fighters," senior Russian military officer Sergei Rudskoi said in Moscow.

The truce would run from 0800 to 1600 local time (0500 GMT to 1300 GMT) "in the area of Aleppo," Rudskoi said.

"During this period the Russian air force and Syrian government troops will halt air strikes and firing from any other types of weapons." The announcement came as EU foreign ministers condemned the ferocious air war waged on Aleppo over the past three weeks.

The EU ministers said they would press ahead with extending sanctions against Syrian President Bashar al-Assad’s regime, but stopped short of threatening measures against Russia.

EU foreign affairs chief Federica Mogherini called Moscow’s announcement "positive" but not long enough to allow humanitarian aid to reach the besieged city.

"It can be a start... for sure it is a positive step," she told reporters at the close of the ministerial meeting in Luxembourg.

"The latest assessment from the aid agencies (however) is that 12 hours is needed so work is needed to find common ground," she added.

UN spokesman Stephane Dujarric also welcomed the truce announcement but stressed the "need for a longer pause in order to get the aid in." Once Syria’s thriving commercial hub, Aleppo has been ravaged by air raids and intensifying clashes as regime forces fight to capture the rebel-held east.

Russian air support for the onslaught – which has destroyed hospitals and other civilian infrastructure – has spurred the accusations of potential war crimes.

US Secretary of State John Kerry met his counterparts from Russia, Iran and Syria’s neighbours in Switzerland on Saturday, before flying to London for talks with the British and other European foreign ministers.

Kerry said the Lausanne meeting produced new ideas on reviving a truce, after a ceasefire jointly brokered by Moscow and Washington collapsed last month, but said high-level contacts to flesh them out would continue Monday.

Syria’s war has devolved from a widespread protest movement against Assad’s rule to a multi-front war between rebels, jihadists, Kurds and regime forces.

Turkish-backed rebels dealt a major symbolic blow to the Islamic State jihadist group on Sunday by overrunning the northern Syrian town of Dabiq.

Across the border in Iraq, Prime Minister Haider al-Abadi announced the launch Monday of a long-awaited operation to recapture Mosul – IS’s last major stronghold in the country.

In June 2014, IS declared a self-styled Islamic "caliphate" in territory straddling Syria and Iraq. — AFP