Asked by members of the European Parliament to explain why Assad's name was not on a list of 13 Syrian officials hit by European Union sanctions, Ashton said "we started with 13 people who were directly involved" in cracking down on protests.

"We'll look at it again this week," she added.

"I assure you that my intention is to put the maximum political pressure that we can on Syria."

The 27-state EU on Tuesday issued a range of sanctions including an arms embargo and a travel ban and assets freeze targeting Assad's brother and inner circle.

Ashton had warned the Syrian leader that he could be next.

Assad's younger brother Maher al-Assad, 43, was on the list of senior officials slapped with sanctions along with four of the president's cousins.