Washington's Mid-East envoy George Mitchell has said Syria has a "crucial role" in finding a comprehensive peace settlement, during a visit to Damascus.
The comments came as he held talks with Syria's President Bashar al-Assad in the Syrian capital.
The visit marks a further thaw in relations between the two countries since Mr Obama took power in January.
Correspondents say the US is testing Syria's support for America's stated new drive for peace in the region.
"Syria has an integral role to play in reaching comprehensive peace," Mr Mitchell said on Saturday.
But Mr Mitchell has assured the Lebanese government that securing Syrian co-operation will not come at Beirut's expense.
He arrived in Syria from Beirut, and has already visited Israel, the West Bank, Egypt and Jordan.
On Friday US military officials held talks with Syrian officials in Damascus, which are thought to have included discussions about neighbouring Iraq, Reuters news agency reported.
Mr Obama has said he wants to broker a peace deal with Syria and Israel to end decades of regional conflict.
Improved relations with the US could mean a lifting of sanctions and many new business deals - something many ordinary Syrians are hoping for.
Lina Sinjab, in Damascus
The first high-ranking US visit is likely to be followed by many more.
The United States is now talking directly to the country once isolated by the Bush administration.
"We are here to talk directly to the Syrians and hear directly from them on issues of concern and not to dictate them on any policies," said a State Department official travelling with Mr Mitchell.
Talking directly to the Syrians does not mean that all the issues will be solved overnight. There are still many areas to work on.
The BBC's Lina Sinjab in Damascus says Syria also wants a US ambassador to be appointed after the last ambassador was withdrawn following the assassination of Lebanon's former prime minster Rafiq Hariri.
She says the Syrian government and people want to see US pressure on the Israelis to deliver long-awaited promises of peace.
The Syrians have also promised to reopen an American cultural centre closed after a US raid last year into Syrian territory against suspected al-Qaeda militants.
Mr Mitchell's visit comes just a week after President Obama's ground-breaking speech in Cairo, in which he called for a "new beginning" between Muslims and the US, and vowed to pursue aggressively an end to the Israeli-Palestinian conflict.
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