Sen. Bill Nelson, a member of the Armed Services and Foreign Relations committees, met with Assad after the State Department said that it disapproved of his trip. The United States has limited diplomatic ties with Syria because of its support of Hezbollah and Hamas, which the U.S. deems terrorist organizations, and President Bush has expressed reluctance to seek help from Damascus on Iraq until the Syrians curb that support and reduce their influence in Lebanon.
Assad "clearly indicated a willingness to cooperate" in controlling its border with Iraq, Nelson told reporters in a conference call following the meeting with Assad. The U.S. says foreign fighters often enter Iraq across that boundary.
Nelson said he reported the information to embassy officials and will brief his congressional committees on the trip. He said he expects Sens. John Kerry, Christopher Dodd and Arlen Specter to also visit Syria.
The White House said it does not encourage members of Congress to travel to Syria.
"We don't think that members of Congress ought to be going there," White House press secretary Tony Snow said, adding that the United States continues to denounce Syria's meddling in Lebanon and its ties to terrorist groups.
"We've talked to Syria. We have diplomatic relations with Syria. I think it's a real stretch to think the Syrians don't know where we stand or what we think. It's not as if there's been failure to communicate. The communication has been crystal clear.
The diplomatic push from Congress comes on the heels of a recommendation by a bipartisan panel that the U.S. engage Iran and Syria on the war in Iraq. Bush has remained cool to the proposal by the Iraq Study Group, which was led by former Secretary of State James A. Baker III and former Rep. Lee Hamilton.
Nelson said he ultimately received logistical support from the State Department in what he called a "fact-finding trip" across the Middle East, being transported by embassy officials from Jordan's capital city of Amman to Damascus. Prior to heading to Damascus, Nelson met with top Israeli and Palestinian officials; in coming days, he plans to visit Qatar, Saudi Arabia, Bahrain and Iraq.
Nelson said he was not interested visiting Iran "at this time." He did not say why.
However, the senator did say that raised the issue of a nuclear-armed Iran to Assad, saying "he ought to understand that that's not only a threat to him, Syria, but to the entire world. . . . He took note," Nelson said.
The senator said he also expressed to the Syrian leader the problems caused by Hezbollah and Hamas and urged Assad to support the release of captured Israeli soldiers. Nelson said the Syrian president responded by saying Israel had 20 Syrians in captivity, one of whom died recently from leukemia.
The senator shrugged off suggestions he was challenging Mr. Bush's authority by sidestepping the Republican administration policy that the U.S. have no contact with Syrian officials.
"I have a constitutional role as a member of Congress," Nelson said.
Meanwhile, Mr. Bush criticized Damascus anew and called on it to free all political prisoners.
In a statement, the president expressed support for the Syrian people, and said they "deserve a government whose legitimacy is grounded in the consent of the people, not brute force."
The U.S.-backed government in Lebanon led by Prime Minister Fuad Saniora is being challenged by the Hezbollah-led, pro-Syrian opposition. Mr. Bush said Syria should disclose the fate of the many missing Lebanese citizens who disappeared following their arrest in Lebanon during decades of Syrian military occupation.
"The Syrian regime should immediately free all political prisoners, including Aref Dalila, Michel Kilo, Anwar al-Bunni, Mahmoud Issa, and Kamal Labwani," Mr. Bush said. "I am deeply troubled by reports that some ailing political prisoners are denied health care while others are held in cells with violent criminals."
The White House said the statement was issued in connection with Human Rights Day this week.
"It's important to remind people that Syria remains an aggressive violator of human rights," Snow said. "It's also important to draw attention to their role in trying to undermine the democratic government in Lebanon and tell them we expect better."