Syrian officials have denied a U.S. military accusation that insurgent leaders in Iraq, loyal to Abu Musab al-Zarqawi, met last month in Syria.

A foreign ministry official, speaking to VOA in Washington Thursday, said Syria has been doing its best to stop insurgents infiltrating Iraq since last year.

He said Damascus has asked Washington for more cooperation on the security and intelligence fronts, saying Iraq's security is a concern to everyone in the region.

On Wednesday, an American military official linked the alleged meeting in Syria to a recent spike in insurgent attacks, which have killed more than 400 people in Iraq since the beginning of May.

Meanwhile, violence in Iraq Thursday killed at least 13 people, including a U.S. soldier.

And Iran's foreign minister visited Iraq's highest Shi'ite authority, Grand Ayatollah Ali al-Sistani, at his home in Najaf.  There were no details of the meeting, but both men have called for calm.