» (AP) — Four bombs ripped through Shiite neighborhoods in Baghdad Thursday evening, killing at least 40 people in the worst violence the capital has seen in months, Iraqi officials said. An American civilian aid specialist working to improve education in Iraq was killed in a separate attack.

The violence underscored the fragile nature of the security gains in Iraq at a time when American forces are preparing to withdraw by the end of this year and the challenges facing the State Department personnel and American contractors who would continue on after the U.S. military is gone.

The first three bombs went off in quick succession in a southwestern Baghdad neighborhood shortly after 7 p.m. One targeted a Shiite mosque, another exploded just outside a popular market, while the third went off inside the market where people were doing their evening shopping ahead of the Muslim weekend, Iraqi police officials said.

The officials said 34 people died and 82 others were injured in the three blasts. An official from Baghdad’s Yarmouk hospital confirmed the casualty figures.

An Iraqi resident, Jabir Ali, said he was about 200 yards (meters) away when one of the bombs went off near a barber shop where his cousin works.

"I saw many people killed and injured. I went to see my cousin. The glass at his shop was broken and he was injured in his head, chest and hand by the glass," said Ali, who drove his cousin to the hospital.

About an hour later, a parked car bomb targeting a police patrol killed six people, including one policeman and five bystanders in a different neighborhood in southwestern Baghdad, said hospital officials.

The officials all spoke on condition of anonymity because they were not authorized to speak to reporters.

There was no immediate claim of responsibility, but Sunni extremists such as al-Qaida in Iraq generally tend to target Shiite mosques and neighborhoods and Iraqi security forces.

It was the worst attack in the capital since a parked car bomb exploded near a mourning tent in a northern Baghdad neighborhood in January, killing 48 people.

The American civilian killed earlier Thursday was Dr. Stephen Everhart, said a U.S. State Department spokeswoman, Victoria Nuland.

"Dr. Everhart was an American citizen who was working in Iraq for an implementing partner of the United States Agency for International Development’s Mission in Iraq. He was killed while working on a project to introduce a new business curriculum to a Baghdad university in a program supported by the Iraqi Ministry of Higher Education," she said in a statement.

"We are saddened by this tragedy and extend our thoughts and prayers to Dr. Everhart’s family and loved ones, and to the three other injured victims and their families," she said.

Everhart worked at the American University in Cairo, where he was associate dean of the Business School and a finance professor. Before joining AUC, he worked extensively with the World Bank and the Overseas Private Investment Corporation, a U.S. government agency designed to help businesses break into developing markets.

He also wrote articles on topics like international aid, corruption and financial markets.

Officials at Georgia State University said Everhart listed San Antonio, Texas, as his hometown on his registration paperwork. Everhart got both his master’s and doctorate in economics at Georgia State in Atlanta.

Mary Beth Walker, dean of the School of Policy Studies, said Everhart met his wife, Stephanie, while in graduate school there. She described him as a "hard worker" with a good sense of humor.

Walker said Everhart had contact with Georgia State faculty members in the last two weeks about his work in Iraq and said he was planning to move to Vietnam soon to work at a university there.

The State Department gave no information about how he was killed, but an Iraqi police official said the American contractors were visiting a satellite office of Mustansiriyah University in eastern Baghdad when they were hit by a roadside bomb.

It was not known whether the assailants knew Americans were in the convoy or not. It is extremely rare for an American working so closely with the State Department to be killed.

Shiite militias who operate in the nearby neighborhood of Sadr City have stepped up attacks against the U.S. military in recent months and threatened violence against other American targets. Nine American soldiers have been killed in Iraq so far this month, one of the highest death tolls in two years.

The U.S. military has also accused Shiite militias of lobbing mortars and rockets at the U.S. Embassy in the Green Zone.

Shiite militias are trying to claim they are driving the U.S. military from Iraq and make the U.S. think twice before agreeing to have U.S. troops stay in the country past the Dec. 31 date by which they’re slated to go home.

The attack against Everhart and the other contractors could have serious repercussions for the U.S. Embassy in Baghdad and the ability to conduct operations in the country. Already, U.S. Embassy staff and contractors working with agencies such as USAID generally travel in armored vehicles with guards and sometimes with U.S. military assistance.

Earlier this week, a convoy carrying French Embassy staff was targeted by a roadside bomb in the Karradah neighborhood. No one was killed in that incident.

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Writer Saad Abdul-Kadir in Baghdad and Dorie Turner in Atlanta contributed to this report.