At least nine people were killed and 90 others wounded when forces loyal to Yemeni President Ali Abdullah Saleh opened fire on Saturday on protesters in the capital Sanaa demanding he face trial, a medical source said.Saleh said on Saturday he would go to the United States in order to allow an interim government to prepare for an election to replace him, but did not specify when he would leave.RELATED:Two dead as ceasefire called in YemenYemen's Saleh signs power transfer dealSpeaking to reporters, Saleh said he had no designs on staying in power. "I will go to the United States. Not for treatment, because I'm fine, but to get away from attention, cameras, and allow the unity government to prepare properly for elections," he said."I'll be there for several days, but I'll return because I won't leave my people and comrades who have been steadfast for 11 months," he said. "I'll withdraw from political work and go into the street as part of the opposition."Mohammed al-Qubati, a doctor at a field hospital that has treated protesters during 11 months of mass demonstrations against Saleh, said about 150 people were wounded by tear gas canisters troops fired, or incapacitated from inhaling gas in addition to the 90 wounded.Shots rang out as protesters demanding that Saleh face trial entered the city chanting "No to immunity," at the climax of a mass march that started days earlier in the southern city of Taiz, said residents.The protesters were referring to a deal granting Saleh immunity from prosecution for his part in a violent crackdown on months of demonstrations against his 33-year rule.The agreement, crafted by Yemen's wealthier neighbors in the Gulf Cooperation Council (GCC), was designed to ease Saleh out of power and avert civil war in a country that has seen a growing infiltration from al-Qaida and sits next to key oil shipping lanes.Under the deal, Saleh has transferred his powers to his deputy. An interim government will prepare the country for an election to replace him in February, and separate pro-Saleh troops from militiamen loyal to tribal leaders and rebel army units in Sanaa and elsewhere.Protesters, many of them young, chanted "For shame, the blood of the martyrs has been sold for dollars", referring to the immunity deal, which was endorsed by a coalition of opposition parties that are part of the interim government. Witnesses said troops loyal to Saleh spread out across the entrances of streets leading to his compound to block any attempt by protesters to approach it.Pro-Saleh troops also used tear gas in an attempt to turn back protesters in the Sabaeen district of the capital, the witnesses said.Later in the day, marchers retreated and headed towards Change Square, a rallying point for the protests which began in January, they added.Tanks, troops and armored vehicles were deployed around the presidential compound.Protesters want the government to be purged of members of Saleh's family, who still hold key posts in the military and security forces.The new government faces multiple challenges including resurgent separatist sentiment in the south, formerly a socialist republic that fought a civil war with Saleh's north in 1994 after four turbulent years of formal union.The region is also home to Islamists who have seized chunks of Abyan province. Ensuing fighting with government troops has sparked mass flight, compounding a humanitarian crisis in a country with about 500,000 internally displaced people. Top oil exporter Saudi Arabia shares US fears that more instability could embolden al-Qaida's branch in Yemen.The transition deal, should it stick, would make Saleh the fourth leader to surrender power after mass protests that have redrawn the political map in North African and the Middle East.