The West African bloc, Ecowas, wants to send 3,000 troops to Mali.

"Before endorsing an Ecowas force, we would need a clearer plan, more information about what the objectives are, and more evidence that such a force would have a reasonable chance of meeting those objectives," he said.

Mali's neighbours have lobbied for the UN to back their proposed force, fearing the spread of Islamist militancy from northern Mali.

The Ansar Dine group, which is said to have links to al-Qaeda, seized control of Timbuktu earlier this year.

It has already destroyed several of the city's shrines, saying they contravene its strict interpretation of Islam.

Ansar Dine spokesman Sanda Ould Bamana told the BBC that Islamic law did not allow the building of tombs taller than 15cm (6in).

The UN cultural agency Unesco and Mali's government have called on Ansar Dine to halt its campaign.

Unesco has also expressed concern that valuable artefacts and manuscripts may be smuggled out of the region and has urged neighbouring countries to prevent this.

Timbuktu owes its international fame to its role as a centre of Islamic learning, based in its three large mosques, in the 15th and 16th centuries.

Timbuktu is also known as "City of 333 saints", which originate in the Sufi tradition of Islam.

Ansar Dine's Salafist beliefs condemn the veneration of saints.

The group seized control of Timbuktu in April, after a coup left Mali's army in disarray.

Initially, it was working with secular ethnic Tuareg rebels demanding independence for northern Mali's desert territories but the groups have recently clashed and Islamist forces are in control of northern Mali's three main centres - Timbuktu, Gao and Kidal.