The NYPD is keeping security tight amid news that radical cleric Anwar al-Awlaki was killed in an air strike by U.S. forces in Yemen.

Police Commissioner Raymond Kelly said Friday that police are worried that al-Awlaki has followers in the city "who might want to avenge his death."

The department initially amped up security earlier this month. That action followed reports that Al Qaeda was planning a car bombing to coincide with the 10th anniversary of the Sept. 11 attacks. It has been on high alert ever since.

The measures include assigning more patrol officers to the subways. The NYPD also has set up car checkpoints in Times Square and elsewhere.