Baghdad, Iraq ? In a rare strike on a heavily fortified target in the Iraqi capital, insurgents attacked the country’s Interior Ministry building entrance with automatic gunfire and grenades Monday, killing two police officers and wounding five others.

The ambush came on a day when guerrilla violence spanned the country, from the northern city of Tal Afar to the southern port of Basra. In all, 20 people were killed and another 20 injured.

The violence included a roadside bomb attack on a convoy near Basra that killed two British soldiers. In the Baghdad neighborhood of Saidiyah, a car bomb was detonated near a U.S. military Humvee, wounding four U.S. soldiers, the U.S. military said.

The Iraqi Defense Ministry said Monday that 11 people were killed in a suicide car bomb attack in the Euphrates River valley town of Hit, though it was unclear when the attack occurred. Three of the dead were Iraqi troops.

U.S. military officials have said they expect increased insurgency attacks as the Oct. 15 ratification referendum on Iraq’s draft constitution approaches.

The attack on Interior Ministry police occurred Monday just after dawn. Carloads of insurgents stopped on an overpass overlooking the entrance to the Interior Ministry building, a police lieutenant said, speaking on the condition of anonymity.

The gunmen then opened fire and lobbed several hand grenades at Iraqi police officers posted at the ministry’s entrance, about a half-mile from the ministry building, the police lieutenant said. The Associated Press reported that the insurgents used rocket-propelled grenades, not hand grenades, in the attack.