Baghdad ? A roadside bomb killed a U.S. soldier Wednesday in Baghdad, making May the deadliest month for the American military since September.

Also Wednesday, the government’s watchdog agency announced that nearly 1,000 arrest warrants have been issued this year as part of a crackdown on corruption. They include warrants for nearly 50 senior civil servants, the agency said.

The fatal attack occurred two days after a blast struck a U.S. convoy west of the capital, killing three Americans, including two civilians and a soldier.

The spike in deaths comes as U.S. forces face a June 30 deadline to pull back from urban areas as part of a U.S.-Iraqi security pact that took effect this year.

At least 20 American service members have died so far this month, compared with 25 in September, according to an Associated Press tally.

The 20 deaths include five service members killed in a May 11 shooting at a mental health clinic in Baghdad. Sgt. John M. Russell has been charged with murder in the case.