The UN secretary general, Ban Ki-moon, was in talks Wednesday with the Arab League in the hope of agreeing on a new Syrian peace envoy to replace Kofi Annan and keep open an alternative to the spiralling levels of violence.

Western diplomats said Mr. Ban hoped to make an announcement this week, and there was speculation he was leaning towards a Nordic candidate such as one of the former Finnish presidents Tarja Halonen or Martti Ahtisaari. It is unclear, however, whether the Arab League has agreed. Whoever is chosen would - like Mr. Annan, who steps down at the end of the month - have to represent both the UN and the Arab League.

“Diplomats around the UN wonder why anyone would want to take the job,” said Richard Gowan, a expert on international peacekeeping at New York University. “Some western officials think that replacing Annan at all is a bad idea, as it will create further false hopes about a peace deal that the UN simply can't deliver. There is an argument that a fairly low-profile envoy should replace Annan, whose celebrity arguably got in the way of his diplomatic efforts. A lower-level figure might be able to make more progress.”

Mr. Ban himself is said to harbour doubts about what a new envoy could achieve, faced with escalating violence and deep and persistent splits between the permanent members of the UN security council.

His spokesman Martin Nesirky said: “The secretary general is in close, almost daily, contact with the secretary general of the League of Arab States on the work that needs to go into the selection of a successor to Kofi Annan.”

Announcing his resignation last week, Mr. Annan blamed “finger pointing and name calling” in the Security Council for the lack of progress, and insisted Syria's leader, Bashar al-Assad, “must leave office”. The former Secretary General argued that the regime’s “intransigence and refusal to implement the six-point peace plan has been the greatest obstacle to any peaceful political process”.

Russia and China refuse to agree to any UN measure that threatens punitive measures against the Assad regime. The US, Britain and France believe that only the threat of further isolation - they rule out direct military intervention - would change the regime's mind.

There are also deep international divisions on the future of the small UN observer force still in Syria but largely unable to function. Its mandate expires on 19 August. Russia and China want to renew the mandate in its existing form, but western states argue that would simply provide a figleaf for further atrocities against the civilian population. The UK wants to turn the UN mission in Damascus into a more political body, focusing on keeping lines of communication open between the warring parties.

In the interregnum between Mr. Annan and his unnamed successor, there are few signs there will be any dramatic diplomatic breakthroughs. The pace is being dictated by events on the ground, and governments in the neighbourhood and beyond have been struggling to keep place.

Russia

Moscow maintains its full support for Mr. Assad and has been the regime's main arms supplier. It has vetoed all attempts to impose punitive measures on the government. If Mr. Assad's grip on power continues to deteriorate some believe Moscow will go back to the Security Council to cut a deal that would guarantee its hold on its naval base at Tartus.

Iran

Of Syria's neighbours, Iran is the most deeply involved in the conflict. It has admitted the presence of Revolutionary Guard units in Iran. Mr. Annan sought to draw Iran into dialogue on Syria's fate, but the US objected to Tehran's participation. The supreme leader, Ali Khamenei, has underlined his personal support for Mr. Assad by sending his representative, Saeed Jalili, to Damascus.

The US

The Obama administration has largely given up on the UN as a route to a political settlement, and has gradually increased its support to the opposition. US intelligence agents are reportedly operating on the Syrian border in conjunction with the Turkish authorities, principally to ensure the increasing flow of arms into Syria does not end up in the hands of al-Qaeda.

The UK

The British Foreign Secretary, William Hague, is due to issue a statement on Friday raising the level of non-lethal British support to the Syrian opposition. Increasing that support, in the form of communications equipment and training of human rights monitors, has been directed at local groups inside Syria rather than the deeply divided Syrian National Council.

France

Francois Hollande's government has come under fire at home for the lack of diplomatic progress. His predecessor, Nicolas Sarkozy, broke his silence on Wednesday for the first time since his election defeat in May to call for a tougher stance against Damascus, comparing the situation with Libya “where at least I took action”. Mr. Hollande has sought to step up France's diplomatic efforts. The foreign minister, Laurent Fabius, is due to tour the region later this month, visiting Jordan, Lebanon and Turkey. France has called for UN security council members to review the situation on 30 August.

French diplomats concede that in the face of fierce Russian resistance to a tougher UN stance, there is unlikely to be a breakthrough, but they also point out that the situation on the ground could have changed

dramatically in the next 20 days.

Turkey

The Turkish government has provided the main haven for the rebel Free Syrian Army (FSA), but has also sought to keep strict limits on the flow of arms across the border. The policy mirrors ambivalence inside Turkey, pitting the desire to get rid of Mr. Assad against the fear of the chaos that might follow his downfall.

Qatar and Saudi Arabia

The Gulf Arab states have taken the lead in channelling arms and training to the FSA, but have chafed at the lack of US enthusiasm for the effort and at Turkish limits on arms supplies. Consequently, despite the expenditure, the rebels are still reported to be short of ammunition and forced to pay inflated sums for small arms on the black market.

Salman Shaikh, the director of the Brookings Doha Institution, said: “There is a danger of privatised efforts and a security vacuum. There needs to be one channel.”

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