The United States has called on Syria to stop what it calls the arbitrary detention of pro-democracy and human rights activists.
Syria has been putting its own views at the Bahrain summit
Secretary of State Condoleezza Rice made the call at a summit of foreign ministers in Bahrain aimed at promoting reform in the Arab World.
President George W Bush earlier called on Syria to "stop exporting violence and start importing democracy".
Responding to the criticism, Syria accused the US of a "hidden agenda".
"I expect everything because they build their policies on a hidden agenda," Foreign Minister Farouq al-Shara told reporters in Bahrain without giving details.
Ms Rice, currently on a tour of the Middle East, said Washington continued to support what she described as the aspirations of Syria's people for liberty, democracy and justice.
She called for the freeing by Damascus of all prisoners of conscience including Kamal Labwani, who was arrested earlier this month after returning from a visit to the US.
Rice will also visit Saudi Arabia, Israel, the West Bank and Jordan
She also repeated a demand for Syria to co-operate fully with the United Nations inquiry into the assassination of former Lebanese Prime Minister Rafik Hariri in February.
"They should stop trying to negotiate and co-operate," she told reporters travelling with her on her tour, which began in Iraq.
Syria's foreign minister said his country would "fully co-operate" with the inquiry and had "no reservations except concerning the sovereignty of Syria".
Arab foreign ministers at the Bahrain summit insisted the resolution of the Israeli-Palestinian conflict was central to building democracy in the Middle East.
Ms Rice is also due to visit Saudi Arabia, Israel, the West Bank and Jordan during her 10-day trip.