Yemen's parliament approved a law on Saturday granting outgoing President Ali Abdullah Saleh immunity from prosecution, part of a deal for him to step down after nearly a year of unrest.

Protesters and the opposition have accused the security forces, controlled by the president and aides, of using troops and snipers to kill hundreds of demonstrators who, inspired by revolts elsewhere in the Arab world, began protesting against his rule last January.

Lawmakers also backed Vice-President Abd-Rabbu Mansour Hadi as the candidate for all parliamentary parties in a presidential election next month to replace Saleh, in power for 33 years.

The immunity law, backed by a majority, stops short of giving full protection to Saleh's aides after being amended to say they would have immunity only for "politically motivated" crimes committed carrying out official duties, not for those considered "terrorist acts."

A United Nations envoy welcomed the amendment limiting the immunity, which UN human rights chief Navi Pillay has said could violate international law.

"I am pleased that immunity law has been modified but it does not go far enough. The scope of the law is still too broad. The UN cannot condone a broad amnesty that covers UN classified crimes against humanity, genocide, war crimes, gross violations of human rights, and sexual violence," Jamal Benomar said.

"We would have been more satisfied if these recognized categories of crimes were incorporated into the draft law."

Human Rights Watch was far more critical. "This law sends the disgraceful message that there is no consequence for killing those who express dissent," said HRW regional director Sarah Leah Whitson.

"The Yemeni government should be investigating senior officials linked to serious crimes, not letting them get away with murder," she added.

The deal, part of the plan hammered out by Yemen's wealthier Gulf neighbours to ease Saleh from power, will cover Saleh's entire presidency and cannot be cancelled or appealed.

Neighboring top oil exporter Saudi Arabia and the US had backed autocratic Saleh for much of his rule, but endorsed the transition deal, fearing continued unrest would be exploited by al Qaeda's Yemen-based regional wing, seen by Washington as the network's most dangerous branch.

A Middle Eastern diplomat involved in the discussions over Saleh's fate told Reuters on Friday the president still planned to visit the United States for medical treatment but would not leave Yemen permanently.

Al Arabiya television said on Saturday that Saleh planned to visit Oman and Ethiopia before going to the United States for a medical check-up.

A senior Yemeni official said Saleh would have diplomatic immunity if and when he travelled to the United States.

"We are waiting for a third country to approve the president's short visit prior to travelling to the US," said the official, who is not authorized to speak to the press and so declined to be named. The official suggested that the third country was an Arab nation.

Some activists said the immunity deal showed that the successes of the protests could easily be overturned.

"We have lost all faith in the political opposition. If they can grant Saleh this kind of pardon perhaps they will pass more laws against us in the future, maybe next time they will pass laws banning demonstrations. We, as the youth, can no longer trust them," said protest leader Faizah Suleiman.-Reuters