New air strikes on Aleppo as offensive launched

The offensive to retake Aleppo was announced after days of bombardment of rebel-held areas (AP)

Warplanes have carried out fresh air strikes on Aleppo, hours after Syria's government announced an offensive to retake rebel-held areas of the city.

Syrian and Russian planes were pounding eastern Aleppo, according to activists. A rescue worker described what was happening as "annihilation".

The government has urged people to avoid positions held by rebels. Russia has not confirmed its involvement.

US-Russian talks to revive a collapsed truce have broken up without progress.

Russia supports the Syrian government, while the US backs the opposition. The two powers accuse each other of failing to rein in their respective allies on the ground.

The White Helmets, a Syrian volunteer rescue group, says dozens of air strikes were carried out in Aleppo on Friday morning.

The group says the centres set up to help victims of bombardments were being targeted, and three out of four had been put out of action.

The Al Jazeera news agency tweeted that its bureau in the city had been partly destroyed.

Announcing the new offensive on state television late on Thursday, the Syrian government warned Aleppo residents to "stay away" from "terrorist positions".

Syrian military sources said a ground offensive would follow.

One told the Agence France-Presse news agency that the bombardment "could go on for hours or days before the ground operation starts. The timing of the ground operation will depend on the results of the strikes".

Army officials said there would be exit points for anyone, including rebels, who wanted to flee.

The government's warning came after days of air strikes on Aleppo. Syria declared the week-long ceasefire over on Monday.

Residents told the BBC earlier this week that barrel bombs had struck rebel-held districts, causing many fires. Dozens of civilians were reported to have been killed.

Thursday night's meeting in New York brought together members of the International Syria Support Group, which includes the US, Russia and other powers.

After the talks broke down without agreement, UN envoy for Syria Staffan de Mistura described them as "painful and disappointing".

US Secretary of State John Kerry said Washington could not be the only one trying to hold open the door to peace.

Russian Foreign Minister Sergei Lavrov accused US-backed rebels of ignoring the truce, and said a new one would amount to a "unilateral pause".

Also on Thursday, Syrian President Bashar al-Assad denied claims that he was responsible for the ongoing fighting.

In an interview with the Associated Press news agency, he reaffirmed his government's position that a deadly strike on an aid convoy in Aleppo on Monday had not been carried out by Syrian or Russian planes.

Mr Assad also ridiculed concern about the army's use of barrel bombs, saying: "What's the difference between different kinds of bombs? All bombs are to kill, but it's about how to use it. When you use armament... you kill terrorists in order to defend civilians."