Four U.S. troops killed in Baghdad

BAGHDAD, Iraq (CNN) -- Four U.S. soldiers were killed in Baghdad on Thursday, bringing the death toll to 15 so far this week.

A roadside bomb blast killed three U.S. soldiers and wounded 11 others on patrol in eastern Baghdad. Another soldier died and three were wounded in combat in western Baghdad, the U.S. military said Friday.

The number of U.S. troop deaths fell to 80 in July after a three-month period that saw more than 100 fatalities per month.

The U.S. death toll in Iraq now stands at 3,664, including seven civilians from the Defense Department, according to a CNN compilation of U.S. military figures.

Earlier this week, a British soldier was killed in a southern Iraq roadside bombing. The number of British troop deaths in the war stands at 164 and the total coalition toll -- which includes U.S. military deaths -- is 3,959.

Meanwhile, an aide to the highest-ranking Shiite cleric in Iraq was shot and killed, the Iraqi Interior Ministry said Friday.

Fadhel al-Aqel, an aide to Grand Ayatollah Ali al-Sistani, was killed Thursday night in Najaf, a southern Iraqi city that is predominantly Shiite.

Gunmen in a civilian vehicle opened fire on al-Aqel while he was in his car, the ministry said.

About three weeks ago another al-Sistani aide, Abdallah Falak, was stabbed to death while heading to prayers from his house, which is near the ayatollah's residence in Najaf, the ministry said.

Authorities trying to solve the killings are considering a number of factors, including rivalries among Shiites and the possibility of sectarian attacks by Sunnis.

Prime Minister Nuri al-Maliki will travel to Iran and Turkey next week, his office said Friday.

The Islamic Republic News Agency reported that al-Maliki will be visiting Iran on Wednesday, where he and his delegation will discuss economic and political cooperation with officials in Tehran.

The visit to Iran coincides with efforts to develop a U.S.-Iranian-Iraqi security committee.

The visit to Turkey comes as tension simmers along the Iraq-Turkey border, where Turkish troops have massed in the face of attacks from Kurdish separatists, who have bases in northern Iraq. E-mail to a friend

CNN's Raja Razek contributed to this report.

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