The leader of the most powerful Shiite party in Iraq has flown to the United States for further tests to determine if he is suffering from lung cancer, members of his staff said. Abdul-Aziz al-Hakim traveled to the United States on Wednesday after US military doctors advised him to undergo further tests, according to staff members who spoke on condition of anonymity on Saturday because they were not authorized to speak about the issue to the media. Al-Hakim is a key player in Iraqi politics and despite his close ties to Iran, he has been a major partner in US efforts to build a democratic system after the collapse of Saddam Hussein's regime in 2003. American efforts to push through major reforms such as a new oil law, constitutional amendments and expanded opportunities for Sunnis in government would face even more hurdles without al-Hakim's active support. Iraqi President Jalal Talabani also was traveling to the United States for a medical checkup at the Mayo Clinic, a senior Kurdish politician close to the Iraqi leader said Saturday. The 73-year-old Sunni Kurd was hospitalized in Jordan for about two weeks after collapsing three months ago with what doctors called exhaustion and dehydration from lung and sinus infections. Looking pale and slightly unkempt, Talabani met earlier Saturday with visiting British Prime Minister Tony Blair and the two addressed a news conference along with Prime Minister Nouri al-Maliki. Al-Hakim, who quit smoking last year, was examined at a US hospital in Baghdad after complaining of a cough and high blood pressure, the staff members said. They said al-Hakim's office in Baghdad was awaiting results from further tests to be done at a hospital in Houston, Texas. The Washington Post reported Saturday that al-Hakim arrived in Houston on Thursday to meet with specialists at the University of Texas M.D. Anderson Cancer Center. A spokeswoman there, Julie Penne, said Saturday that the hospital would not release any information about whether al-Hakim was a patient there. White House officials, meanwhile, confirmed that the Bush administration had provided assistance to al-Hakim, but gave no details. The members of his staff said he flew to the United States aboard a US military plane. Al-Hakim, 57, wears clerical robes and a turban but he has abandoned seminary studies years ago to concentrate on politics. He took over the leadership of the party after his brother and party founder, Ayatollah Mohammed Baqir al-Hakim, was killed in a massive bombing in the holy city of Najaf in August 2003. The al-Hakim brothers returned to Iraq after Saddam's ouster, ending more than two decades in exile in Iran. Their family has lost more than 60 members during Saddam's 23 years in power, either through executions, torture or assassinations.