DAMASCUS: The head of the now-defunct UN observer mission, General Babacar Gaye left Syria on Saturday after the new international envoy, Lakhdar Brahimi said he was “scared” of the scale of the task he faces to try to end the escalating conflict.

General Gaye left Damascus after the mission officially ended last Sunday in the face of the intensifying violence and the divisions at the UN Security Council over what action to take.

On the ground, the regime pressed on with its campaign against opposition fighters, with activists reporting combat helicopters strafing rebel pockets in the northern city of Aleppo and renewed shelling across the country.

Brahimi, who takes over formally from former UN-Arab League envoy Kofi Annan next month, held talks with UN leaders on Friday, admitting that he was “scared” of the enormity of his mission to try to end a conflict now in its 18th month.

He said the Syrian people “will be our first masters”.

“We will consider their interests above and before anyone else. We will try to help as much as we can, we will not spare any effort,” added Brahimi, a veteran Algerian diplomat who brokered the 1989 accord that ended Lebanon's civil war.

Annan, a former UN chief, ended his six-month bid to bring peace to Syria, complaining of a lack of international support for his efforts to make President Bashar al-Assad implement a peace plan.

The Syrian Observatory for Human Rights said Friday that August was already the deadliest single month of the conflict with more than 4,000 people killed in barely three weeks, and an overall death toll of around 24,500.

Damascus said this week that it was ready to work with Brahimi and voiced hope he could pave the way for “national dialogue” while also suggesting it was ready to discuss Assad's exit as part of any negotiated solution.

Meanwhile, a senior Iranian official arrived in Damascus for talks with Syrian officials, a day after Tehran, the regime's staunchest ally, said it will submit a plan for ending the conflict at a Non-Aligned Movement summit next week.

The West is seeking to increase the pressure on the Assad regime, with Washington and London threatening possible action if Damascus uses its chemical weapons and Paris voicing support for a partial no-fly zone.

Activists say that the regime is intensifying its attacks from the air as it battles to stamp out rebel strongholds in Aleppo and pockets of resistance in the capital.

On the humanitarian front, the UN said on Friday that the flow of refugees fleeing the fighting has jumped, with 202,500 people registering in neighbouring countries, at least a third of them in Turkey.

The UN refugee agency warned that tensions in neighbouring Lebanon, where fighting this week between rival pro- and anti-Assad communities in Tripoli has left 14 people dead, was complicating its efforts to help refugees there.

In Syria, 185 people were killed nationwide on Friday, according to the Observatory, which has a network of activists, doctors and other sources on the ground but whose information cannot be independently confirmed.

Meanwhile, the body of a veteran Japanese war reporter killed while covering the fighting in the battered northern city of Aleppo, was flown home on Saturday.

Mika Yamamoto, 45, was the fourth foreign journalist to have been killed in Syria since March 2011 and the first to have died in Aleppo, which has borne the brunt of the conflict since fierce fighting erupted there last month.

American freelance journalist Austin Tice has also been missing for more than a week, his latest employer the Washington Post said.

In Aleppo on Saturday, the Observatory said helicopters were strafing rebel positions, and reported shelling and fighting in several areas both in the city and the surrounding province.

Rebels said they were digging in for a war of slow destruction in Aleppo, where the regime had warned last month of “the mother of all battles.”

Both the government and opposition forces say attacks on Aleppo province are aimed at cutting arms supply routes to the rebels in Syria's second city.

Rebels claimed earlier this week to control 60 per cent of Aleppo but the regime has dismissed the claims and said on Thursday that the army had recaptured three Christian neighbourhoods, where residents are largely pro-Assad.

In Damascus, troops fired mortar rounds at several areas on the southern outskirts as they pressed what activists said was a renewed bid to crush the insurgency in the capital “once and for all.”