BAGHDAD (AP) – The killings of three U.S. soldiers in separate attacks in Baghdad pushed the American death toll for April up to 47, making it the deadliest month since September.

One soldier died when his vehicle was struck by a roadside bomb. The other died of wounds sustained when he was attacked by small-arms fire, the military said Wednesday.

Both incidents occurred Tuesday in northwestern Baghdad. A third soldier died in a roadside bombing Tuesday night in the east of the capital, the military said.

The statement did not give a more specific location. But the eastern half of Baghdad includes embattled Sadr City and other neighborhoods that have been the focus of intense combat between Shiite militants and U.S.-Iraqi troops for more than a month.

In all, at least 4,059 members of the U.S. military have died since the Iraq war started in March 2003, according to an Associated Press count. “We have said all along that this will be a tough fight and there will be periods where we see these extremists, these criminal groups and al-Qaida terrorists seek to reassert themselves,” U.S. military spokesman Maj. Gen. Kevin Bergner told reporters in Baghdad.

“So, the sacrifice of our troopers, the sacrifice of Iraqi forces and Iraqi citizens reflects this challenge,” Bergner said in response to a question about what’s behind the increase in American troop deaths.

The latest fighting erupted at the end of March after Prime Minister Nouri al-Maliki launched a crackdown against Shiite militias in the southern port city of Basra. But it quickly spread to Baghdad’s Sadr City, a sprawling slum with about 2.5 million people that is a stronghold of the Mahdi Army militia of anti-American cleric Muqtada al-Sadr.

The militiamen have used the district as a base to fire barrages of missiles and mortar rounds at the U.S.-protected Green Zone which houses much of the Iraqi government and Western diplomatic missions, including the U.S. and British embassies. They also have fought running street battles in which hundreds have died. The U.S. military says those killed have been mainly gunmen. But police and medical authorities in Sadr City say innocent civilians have frequently gotten caught up in the fighting.

Such street battles, in tight confines and amid frightened civilians, are increasingly becoming a hallmark of the drive into Sadr City and recall the type of head-on clashes last seen in large numbers during last year’s U.S. troop buildup in Baghdad and surrounding areas.

The Sadr City violence continued overnight with the destruction of a school in the district. AP Television News footage showed that parts of the two-floor Baghdad Girls’ School had pancaked as the result of an explosion. Desks were hanging down from the slanting classrooms where the outer walls were blown out by the blast.

Local officials said the school was the target of an airstrike on Tuesday evening.

An official at the local hospital, who asked not to be named because he was not authorized to release the information, said two people were killed and 16 wounded overnight in Sadr City. He said this brought the death toll in the district since Tuesday to 31, with 107 wounded.

The U.S. military had no comment about the school but said an Abrams tank fired a 120 mm shell at gunmen shooting at U.S. troops in Sadr City, killing all three. In another part of Sadr City, an unmanned drone fired a missile at a group of men planting a roadside bomb and killed one, the military said.

On Wednesday, al-Maliki accused the Mahdi Army of using civilians as human shields, and vowed to continue the crackdown against militias.

“We can’t build a state along with militias,” he told reporters at a news conference. «We want to build a single national army.”

Al-Maliki said gunmen had killed the nephew of police Maj. Gen. Abdul-Karim Khalaf, an Interior Ministry spokesman who had also overseen operations in Basra, by hanging him from an electricity pole in Sadr City.

In another development, the office of Abdul-Aziz al-Hakim, head of the Shiite Supreme Islamic Iraqi Council, said he received a telephone call from U.S. President George W. Bush on Tuesday afternoon.

The SIIC is one of the main members of al-Maliki’s U.S.-supported government and a rival of al-Sadr’s movement.

An SIIC statement said that two exchanged views about the current situation in Iraq. There was no immediate comment from the U.S. Embassy in Baghdad.