The United States and Syria are exploring the possibility of better relations after years of tension - but questions remain over just how much common ground exists between the two. In a sign that President Barack Obama is seeking better ties, several US congressmen have passed through Syria in the last few days, including Sen. John Kerry, who arrived Saturday and met with President Bashar Assad. The State Department also announced Friday it has scheduled a meeting next week with Syria's ambassador to the US to discuss differences between the two countries - the first such meeting in months. US-Syrian relations have long been tense. Damascus' support for Hamas and Hizbullah has drawn the ire of Washington, which has also accused Syria of allowing foreign fighters to cross into Iraq. Syria, which staunchly opposed the 2003 invasion, insists it is doing all it can to safeguard its long, porous border. Relations soured further when the Bush administration pulled the US ambassador out of Syria in 2005 to protest Syria's suspected role in the assassination of former Lebanese Prime Minister Rafik Hariri. Damascus denied involvement in his death, but in the uproar that followed, it was forced to withdraw its troops from Lebanon, ending a 29-year military presence. The congressional delegations, led by Democrats, are carrying the message that America wants to engage countries it has been at odds with if they are willing, as Obama puts it, to unclench their fists. Kerry, who heads the Senate's Foreign Relations Committee, did not speak after his meetings in Syria Saturday. But during his stop in Beirut on Wednesday, Kerry said the US would renew diplomacy with Syria but in return expected Syria to "change its behavior" - particularly on Iraq and Lebanon. "But unlike the Bush administration that believed you could simply tell people what to do and walk away and wait for them to do it, we believe we have to engage in a discussion," Kerry said in Beirut. "And so we are going to renew diplomacy but without any illusions, without any naivete, without any misplaced belief that just by talking, things will automatically happen," the Massachusetts senator added. Besides Kerry, the other Congress members on separate visits were Sen. Benjamin Cardin of Maryland and House Foreign Affairs Committee Chairman Rep. Howard Berman of California. There are concerns that new American openness toward Damascus may only be cosmetic, because the long-standing differences between the countries have not changed much. Syria's ambassador to Washington described the congressional visits to Damascus as being "of extreme importance and depth." But he stressed he was still waiting to see if the visits change "the manner of dialogue between us and America." "Let us see what are the goals we all want to reach, where we agree, where we disagree," Imad Mustapha told The Associated Press in Damascus. Mustapha is to meet with Jeffrey D. Feltman, the acting assistant secretary of state for Near Eastern affairs, according to State Department spokesman Gordon Duguid, in the belief that direct engagement with Syria will advance US interests. "Our concerns include Syria's support to terrorist groups and networks, Syria's pursuit of nuclear and unconventional weaponry, interference in Lebanon and a worsening human rights situation," he said Friday. Already during their trips to the Middle East, Kerry and Cardin repeated the previous American language demanding Damascus change its ways in terms of its ties to Iran and backing of Hizbullah in Lebanon and the Palestinian Hamas. But Assad has sent signals he wants to work with Washington. In an interview with the British newspaper The Guardian published this week, Assad said he was impressed by Obama's friendly gestures and welcomed the US delegations to Syria. But he also said he is still waiting to see results. "We are still in the period of gestures and signals. There is nothing real yet," he said. Syrian political analyst Imad Shueibi was optimistic that US-Syria relations would change from a period of "the wrestling of wills to the sharing of wills." "What is happening is not just checking the pulse," he said of the congressional visits. "It is an attempt to define the possible horizons in the relations ahead."