Morocco has ordered Syria's ambassador to leave the country as president Bashar al-Assad's government troops and rebels battle in the streets of the capital Damascus.

Meanwhile, Russia's foreign minister Sergei Lavrov has accused the West of "elements of blackmail" in putting pressure on Moscow to agree to UN sanctions.

He told journalists before a meeting with UN -Arab League envoy Kofi Annan that taking a harder line on Syria "is not the key" to end violence.

"To our great regret, there are elements of blackmail," Lavrov said. "We are being told: if you do not agree to the resolution under Chapter 7 of the U.N. Charter, then we shall refuse to extend the mandate of the monitoring mission in this country."

"We consider it an absolutely counterproductive and dangerous approach since it is unacceptable to use observers as bargaining chips," he said.

Lavrov suggested an extension of the military observer mission, instead, under a broader mandate.

Meanwhile, Morocco's communications minister Mustapha Khalfi confirmed that he asked Ambassador Nabih Ismael to leave the country.

Morocco is the latest Arab nation to expel its Syrian diplomats.

Iran has offered to host talks between Syria's government and opposition in Tehran. The country's foreign minister Ali Akbar Salehi said he will invite dissidents in a bid to prepare and facilitate the ground for talks between the two factions.

He said that Iran supports the six-point plan proposed by Annan, which has failed to end the bloodshed.

The latest development came as fighting between government troops and the rebel Free Syrian Army ravaged the central Damascus neighbourhood of Midan.

"The rebels are trying to hold the army off in al-Zahra al-Jadeeda (neighbourhood). There is fighting there and the sound of bombardment and rocket-propelled grenades is echoing from there," Radeef, an opposition activist, told the Guardian. "Armoured vehicles are now deployed in the rest of Midan and army snipers have taken positions on rooftops."

Armoured vehicles have entered Midan to boost Assad's troops.

It represents one of the most significant placements of forces in the capital since the uprising started last year.

Midan is a strategic Sunni Muslim neighbourhood.