A suicide bomber blew himself up on Tuesday among dozens of Iraqi army recruits who had gathered near a military headquarters in downtown Baghdad in a devastating strike that killed atleast 51 people and wounded 119.

The massive morning blast took place just outside the former Iraqi Ministry of Defense building that now houses the army’s 11th division headquarters.

The site receives about 250 new recruits each week as Iraqi security forces try to bolster their ranks to prepare for the US military’s looming withdrawal after seven years of war.

The recruits were gathered in an open area next to Maidan Square in central Baghdad as they waited to be let through the main gates in small groups.

Iraqi security forces have been trying to boost their numbers as the US military begins to leave the country.

All but 50,000 US troops will go home by the end of August, with the rest to follow by the end of 2011 under a security agreement between Baghdad and Washington.

But insurgents determined to highlight the Iraqi government’s struggle to protect the nation have been stepping up attacks in recent weeks.