Baghdad ? Roadside bombs killed four U.S. soldiers in northern Iraq, the military said Wednesday, in a spike of violence that pushed to at least nine the number of Americans who have died here this week.

In the latest attack, one soldier was killed by an explosively formed penetrator, or EFP, about 9 a.m. Wednesday in the predominantly Shiite eastern half of Baghdad, the military said. The armor piercing bombs are believed to come from Iran and have been used by Shiite extremists to kill hundreds of American forces.

The U.S. military said three other U.S. soldiers and an Iraqi interpreter were killed late Tuesday by a roadside bomb in the northern Ninevah province, where al-Qaida in Iraq and other Sunni extremist groups remain active.

The four U.S. fatalities brought the monthly death toll for American troops in Iraq to at least 26 – well below figures of last year but an increase over the 19 who died in May, the lowest monthly tally of the war.

In all, at least 4,110 U.S. military service members have died in the Iraq war since it began in March 2003, according to an Associated Press count.

The U.S. military says violence in Iraq has dropped to its lowest level in more than four years, but attacks are continuing as Sunni and Shiite extremists try to regroup and undermine security gains.

“The level of violence has dropped dramatically,” said Lt. Col. Steve Stover, spokesman for the U.S. command in Baghdad. “It has gotten quieter. But that doesn’t make these losses any easier.”

He said militants “are constantly thinking of ways that they can undermine us, undermine the government, undermine the Iraqi security forces.”

The bombing in Nineveh occurred a day after a bombing in a district council office in the Baghdad Shiite district of Sadr City killed four Americans – two soldiers and two government employees.

On Monday, a Sunni gunman waiting in a car killed two U.S. soldiers and an interpreter as they emerged from a meeting with municipal officials in Madain, about 15 miles southeast of Baghdad.