BAGHDAD, – A suicide bomber killed up to 20 people including five policemen and many plain-clothes security guards at a Baghdad restaurant close to the Green Zone government compound on Sunday, several police sources said.

A further 20 were wounded after the bomber walked into the restaurant during lunchtime on a street protected by numerous police checkpoints and a few hundred meters (yards) from one of the main public entrances to the fortified Green Zone, according to Reuters.

The attack came a day after U.S. and Iraqi generals declared success in a month-long campaign, known as Operation Lighting, against insurgent bomb factories and other Sunni rebel activities in the capital.

A wave of suicide car bombings contributed to the deaths of more than 1,000 Iraqis in the weeks following the formation of the Shi”ite-led government in late April. The generals said suicide car bombings had been halved by their operation but warned that rebels were still capable of major attacks.

A series of car bombings at entrances to the Green Zone in December led to security being tightened on the approach roads to the compound. A bomber approaching the restaurant on foot, however, would be less liable to being checked.

The entrance near which the attack took place is a main entrance for civilian employees working in the Green Zone, as well as for journalists and other visitors to the area, which also houses the U.S. and British embassies.