(Adds killing in south)
By Mohammed Ghobari
SANAA Dec 25 (Reuters) - Yemen's acting leader on Sunday urged foes and loyalists of President Ali Abdullah to call a truce, after Saleh's forces killed nine people demanding he be tried for the deaths of demonstrators over nearly a year of protests against him.
Troops from what witnesses identified as loyalist units opened fire on tens of thousands of protesters approaching Saleh's compound in the capital on Saturday after a days-long march from the city of Taiz by protesters chanting "No to immunity!".
They referred to a pledge to spare Saleh prosecution in exchange for giving his powers to his deputy, Abd-Rabbu Mansour Hadi, and letting a government including opposition parties lead Yemen to a February election to replace Saleh after 33 years.
That government is to separate Saleh's forces from rebel army units and tribal militias they have fought in Sanaa, a key to a power transfer deal brokered by neighbouring Gulf states to avert a civil war they fear will affect them.
The state news agency on Sunday quoted Hadi as saying during a meeting with U.S. ambassador Gerald Feierstein that all sides "must commit ... to a truce and respect its rules forbidding escalation" that would threaten the transition deal.
Washington long backed Saleh as a cornerstone of its "counter-terrorism" policy in Yemen, which includes the use of drones to kill alleged al Qaeda members. A CIA drone strike killed Anwar al-Awlaki, a U.S. citizen linked to Al Qaeda's regional wing, earlier this year.
MILITARY DENIES IT KILLED PROTESTERS
Hours after the killings, Saleh said he would leave for the United States and give way to the new government and the vote to pick his successor. But he gave no timetable for leaving and vowed to return in opposition to the government.
"An unstable Yemen means an unstable region. So, protect the security, unity and stability of Yemen, neighbour states," he told reporters. "Its security is yours."
A defence ministry website, September 26, on Sunday cited an unidentified official as denying the military - key units of which are led by Saleh's son and nephew - played any role in the killing of the protesters in Sanaa.
It pinned the blame on the interior ministry - now led by an opposition figure - calling witness and news accounts of pro-Saleh troops shooting protesters "baseless, mendacious claims that are part of a vicious media campaign ... against the defence establishment."
The interim government, led by a former foreign minister who joined the opposition against Saleh, late on Saturday called for an investigation of the killings.
The youth-led protesters who have taken to the streets against Saleh have condemned the opposition parties - some of which once took part in Saleh's governments - for agreeing to grant him immunity. They demand that he and his inner circle be tried and banned from power.
Joe Stork, deputy Middle East director of Human Rights Watch, called on governments to ignore the immunity pledge and freeze Saleh's assets abroad, saying: "Promises of immunity encourage rather than deter illegal attacks."
Any post-Saleh government would face overlapping regional conflicts that have displaced nearly half a million people. Attacks on infrastructure hamper the modest oil exports that fund imports of staple foods.
Fighting with Islamists who have seized chunks of territory in a southern province, Abyan, has sent tens of thousands of its residents to flight, compounding Yemen's humanitarian crisis.
Militants killed a security officer on Sunday night as he got out of his car in the southern port city of Aden, a security source said. The source could not verify the identities of the militants.
Separatist sentiment is also surging in the south. (Additional reporting by Mohammed Mukhashaf; Writing by Joseph Logan and Nour Merza; Editing by Peter Graff)