A Yemeni government proposal to grant President Ali Abdullah Saleh amnesty in return for his speedy exit is an affront to thousands who suffered under his rule and should be rejected by the parliament, U.S.-based Human Rights Watch group said.

Yemen's cabinet proposed the immunity law for Saleh on Sunday to encourage him to step down under a Gulf-brokered plan to end protests that have paralysed the country over the past year.

Washington-based Human Rights Watch said in a statement late on Tuesday that the measure could result in impunity for serious crimes such as deadly attacks on anti-government demonstrators in 2011.

Passing this law would be an affront to thousands of victims of Saleh's repressive rule, including the relatives of peaceful protesters shot dead last year, said Sarah Leah Whitson, the group's executive Middle East director.

Yemeni authorities should be locking up those responsible for serious crimes, not rewarding them with a license to kill.

U.N. human rights commissioner Navi Pillay has also voiced objections to the draft. However, the United States has defended it, saying the immunity provisions were negotiated as part of the Gulf Cooperation Council deal to get Saleh to leave power.

Under the arrangement, Saleh's General People's Congress party (GPC) and the opposition Joint Meeting Parties (JMP) agreed to divide up cabinet posts between them, forming a national unity government to lead the country towards presidential elections in February.

The United States and Saudi Arabia are keen for the plan to work, fearing that a power vacuum in Yemen is benefiting militants alongside the Red Sea, an important shipping channel.

The draft law, which parliament is expected to debate as early as Wednesday, violates Yemen's obligations under international law to investigate and prosecute serious crimes such as torture, war crimes, and crimes against humanity, HRW said.

HRW also said immunity would not prevent courts in other countries from prosecuting serious human rights crimes in Yemen under universal jurisdiction laws. Even if the Yemeni parliament grants immunity, the law will not hold water abroad, Whitson said.

HRW said there had been a total of 270 confirmed deaths of protesters and bystanders in 2011 during attacks by government security forces and gangs on largely peaceful demonstrations, mainly in Sanaa.

From north to south to central Sanaa, the Saleh government has violated the basic rights of the Yemeni people, Whitson said. Without accountability for these crimes, there can be no genuine break from the past in a post-Saleh Yemen.

Yemeni prime minister Mohammed Basindwa visited Saudi Arabia on Tuesday and is scheduled to meet other Gulf Arab leaders this week to discuss the transition of power in a country that has become a base for a branch of al Qaeda.

(Reporting by Martina Fuchs; Editing by Ben Harding)