Abdel-Aziz al-Hakim, who heads the Supreme Council for the Islamic Revolution in Iraq, a Shiite Muslim group, also said sending Turkish peacekeepers to Iraq (search) will not solve the country's security crisis.
American troops should "leave as soon as possible because there are no people who believe in occupation and accepts occupiers," said Al-Hakim, whose elder brother and Shiite leader, Mohammed Baqir al-Hakim, was killed in an August bombing in the Iraqi holy city of Najaf (search).
Al-Hakim's three-day visit to Syria, which for a long time was a close ally of his group, comes a week after Israeli warplanes attacked a camp near Damascus that Israel claimed was a training center for the Palestinian militant group Islamic Jihad (search).
Syria denied the allegations and said Palestinian militants abandoned the camp years ago.
"Iraq and Syria, people and states, are brotherly, and their fate is the same. Therefore, we stand by their side," al-Hakim told reporters. "When there is an aggression against Syria, it is an aggression against Iraq."
Syria, which is ruled by a rival faction of Saddam Hussein's Baath Party, had close relations with Iraqi groups that opposed the ousted leader, and most Iraqi opposition groups had offices in Damascus.
Asked if he considers attacks against U.S. troops to be terrorist acts, al-Hakim said, "We believe that many of these operations are terrorist acts because they target civilians, scholars, oil and water installations and public establishments.
"We consider these operations terrorist acts and increase instability in Iraq. They are harmful and are rejected by Iraqi people," he said.
Although anti-American attacks have left 96 U.S. soldiers dead since May 1, when President Bush declared major combat over, bombings have also killed scores of civilians and saboteurs have targeted the country's infrastructure.
Al-Hakim, who is scheduled to meet Syrian President Bashar Assad on Tuesday, said he does not think sending Turkish peacekeepers to Iraq will help in easing the bad security situation.
"We are not for the entrance of any forces," he said. "We believe that the severe security problem in Iraq is because of the wrong policies of American forces and occupation forces. The only treatment for this problem is to depend on the Iraqi people."
Turkey's parliament gave permission last week for the government to send troops to Iraq, but Iraqi Kurdish groups and Governing Council members have opposed the move, saying peacekeepers from neighboring countries could interfere with Iraq's postwar development.