Navi Pillay, the UN human rights chief, has expressed alarm at what has been described as the disproportionate use of force by Yemen authorities against protesters.

The UN human rights office said on Friday that Yemen had approved a mission to examine the violence during the anti-government protests in the country.

A spokesperson for the UN High Commissioner for Human Rights said that it had "been seeking access" and that "yesterday we received confirmation from the permanent mission [embassy] in Geneva that we can do a mission to Yemen".

The spokesman said: "They [the Yemen government] suggested we visit at the end of June; we would like to go rather earlier than that, and we stand ready to deploy as soon as we can."

Earlier on Friday, a military vehicle was attacked near the town of Maarib, killing five Yemeni soldiers from a unit under the command of General Ali Mohsen, who defected to protesters last month.

A security official said the vehicle was ambushed with a rocket-propelled grenade, and that Yemen suspects the attack was carried out by al-Qaeda fighters.

Saleh's party said in a text message distributed by the Saba news agency that it welcomed Qatar's decision, after the president had accused the Gulf country of inciting months of demonstrations aimed at unseating him.

A government source, who asked not to be identified, said: "Yemen will continue working with the rest of its brothers in the GCC for the success of the initiative."

Recent developments in Yemen have strongly damaged the economy in the Arab world's poorest country.

The months of protests have cost the economy $5bn, or about 17 per cent of Yemen's 2009 gross domestic product, Hisham Sharaf, the trade and tourism minister, said.

"Several oil companies have quit the country and the refineries in the southwestern governorate of Aden came to a standstill a week ago," said Amir al-Aidarou, the oil minister, adding that many foreign oil workers had left Yemen.

Aidarou said: "If the problem persists, the government will be unable to meet the minimum needs of the citizens. The situation will pose a catastrophe beyond imagination."