The US Secretary of State, Condoleezza Rice, has met the Syrian Foreign Minister, Walid Muallem, and has asked him to take action to prevent foreign fighters from entering Iraq.
The groundbreaking meeting took place on the sidelines of a summit on Iraq in Egypt.
It is the first time the two countries have held such a high-level talks since the death of the former Lebanese Prime Minister, Rafik Hariri, in 2005.
Syrian officials have been linked to his killing, but Damascus has denied any involvement.
Washington has also accused Syria of stoking violence in Iraq, but says it has recently showed signs of changing.