Unrest Shakes Aleppo as Rebels Say Ceasefire Plan 'Dead End'

Heavy clashes and a regime barrel bomb attack shook the Syrian city of Aleppo Thursday after rebels tried to seize an intelligence headquarters in a forceful rejection of U.N. ceasefire efforts.

The fresh violence came during a visit to Aleppo by a delegation sent by U.N. envoy Staffan de Mistura, who is seeking to "freeze" fighting in the devastated northern city.

Wednesday's attack on the air force intelligence offices, which left at least 20 members of regime security forces and 14 rebels dead, was the worst unrest in Aleppo since the opposition rejected the peace plan on Sunday.

Samir Nashar, a member of the opposition National Coalition who is in contact with groups who attacked the regime building, said the assault "sends a clear message to the regime and to De Mistura" that the rebels reject his initiative.

"De Mistura is at an impasse and is facing a dead end," Nashar told Agence France-Presse.

The attack was followed Thursday by heavy clashes between Syrian regime forces and rebels near the intelligence offices on Aleppo's western edge, a monitor and security source said.

"There are very heavy battles between regime forces and (rebel) fighters in the area of yesterday's attack," Rami Abdel Rahman, the director of the Britain-based Syrian Observatory for Human Rights, told AFP.

A Syrian military source said the army had launched an attack "against (rebel) gunmen positions, killing and wounding many of them" in the area.

- Rebels 'suspicious' of peace effort -

Regime forces also struck rebel-held territory in the east of the city, the Observatory said, killing at least 18 civilians in a single barrel bomb attack.

This followed rebel shelling on regime neighborhoods on Wednesday that killed nine civilians, including three children and two women. 

Fighting in Aleppo erupted in mid-2012, and control of the city -- once Syria's commercial hub -- has since been divided between rebels on the eastern side and the regime in the west.

De Mistura has made the plan for a temporary ceasefire in Aleppo the centerpiece of his efforts to bring any kind of halt to the conflict in Syria, where more than 220,000 people have been killed since it erupted in March 2011.

He held talks in Damascus on Saturday to try to finalize a deal and then sent the delegation to Aleppo to meet the opposition.

But Nashar said rebels had no intention of holding talks with delegation members.

"De Mistura's initiative does not address even the minimum of rebel demands," Nashar said.

The rebels have refused to consider the proposal unless it forms the basis for a "comprehensive solution" to the conflict through the departure of President Bashar Assad.

Nashar said opposition forces are "suspicious" of the U.N. envoy's intentions and see his efforts as "trying to find an opportunity for the regime to breathe in the north."

- Rebels target regime 'backyard' -

De Mistura has particularly angered opposition groups by describing Assad as "part of the solution" to the Syrian conflict.  

They have also demanded the regime cease barrel bomb attacks like the one in Aleppo on Thursday.

Rights groups have criticized the bombs -- crude devices made of barrels packed with explosives and usually dropped from helicopters -- as indiscriminate, citing the large number of civilians killed by them.

Assad has denied the army uses the makeshift bombs.

Wednesday's attack on the intelligence headquarters began with a huge blast, featuring a favored tactic of Syria's rebels of digging tunnels near government buildings and setting off explosives.

The building has been a frequent target for rebel groups, which have repeatedly attempted to make gains in regime-held areas in Aleppo's west.

But Nashar said the attack marks "significant progress in rebel military operations because the intelligence building falls within city limits."

Rebel attacks on these areas, he said, "threaten the regime in its own backyard."

Elsewhere in Syria, seven civilians were killed in a regime air strike near a school in the northern province of Idlib, Abdel Rahman said.

Syria's conflict began as a popular uprising but evolved into a multi-front civil war that has divided the country into a patchwork of fiefdoms controlled by different factions, including the extremist Islamic State group.