Published reports say the chief U.N. investigator into the assassination of former Lebanese Prime Minister Rafik Hariri has summoned six top Syrian intelligence officials to Lebanon for questioning.

The Associated Press and the respected pan-Arab daily, al-Hayat, report that Syrian President Bashar al-Assad's brother-in-law, General Assef Shawkat, is among those U.N. investigator Detlev Mehlis wants to question.

Mr. Mehlis is reported to have sent the request to Damascus on Wednesday through the United Nations.

On Monday, the United Nations Security Council unanimously adopted a resolution (1636) demanding Syria's cooperation with the U.N. investigation, or face "further action."

Mr. Mehlis issued a report last month on his team's findings so far. In it, he linked top Syrian and Lebanese intelligence officials to Mr. Hariri's February assassination.

Some information for this report provided by AP.