An American was found dead in Baghdad's fortified Green Zone, the U.S. military said Saturday, the apparent victim of an unprecedented slaying that occurred at a time when blast walls are coming down and Iraqi forces are assuming greater control.

Another American, believed to be a civilian contractor, was killed Friday night when a rocket struck the Green Zone near the U.S. Embassy, the military said. It was believed to be the first fatal rocket attack there this year.

Those deaths have raised concerns about security before the June 30 deadline for all U.S. combat troops to pull out of Baghdad and other cities. At least 66 people were killed nationwide in a two-day string of bombings this week.

Iraq assumed control of the Green Zone zone on Jan. 1 under a U.S.-Iraqi security agreement, taking primary responsibility from the Americans for searching vehicles and checking identity papers as entry checkpoints.

The Iraqis have begun removing some of the protective blast falls around the Green Zone — part of a campaign to restore a sense of normalcy as violence in the city has waned.

The U.S. military gave few details of the slaying, saying only that an American was found dead Friday in his car and that Army criminal investigators were handling the case. No further details were released.

An Iraqi security official said the victim had been stabbed in his chest and his throat had been slit. He said the body was found lying near a water tank by drivers who had gone there to fill water delivery trucks Friday morning.

The official spoke on condition of anonymity because he was not supposed to release information.

The victim was identified by his brother as Jim Kitterman, 60, of Houston, Texas, who runs a small construction company based in the Green Zone and had worked in Iraq for about six years.

Although Americans and others have been killed in rocket or mortar attacks in the Green Zone, Kitterman was believed to be the first American ever assassinated there since the protected area was established after the city fell to U.S. forces in April 2003.

The victim's brother, Cliff Kitterman, told The Associated Press that U.S. authorities notified him about his brother's death but he refused to give details of what he had been told.

The Washington Post quoted a U.S. official familiar with the investigation as saying the victim had been bound, blindfolded and stabbed multiple times. The newspaper did not identify the official by name because, it said, he was not authorized to release the information.

The 3.5-square mile area in the heart of Baghdad includes U.S. and other embassies, the Iraqi parliament and the prime minister's office. It has been long considered the safest area of the city.

Nevertheless, two suicide bombers struck a cafe and a nearby souvenir shop in October 2004, killing five people. In April 2007, a suicide attacker detonated an explosives vest inside the Iraqi parliament cafeteria in the Green Zone, killing a Sunni lawmaker and wounding 22 other people.

In 2005, Ronald Schulz of Anchorage, Alaska, was believed to have been kidnapped from the Green Zone where he was working as an electrician. His body and that of a woman believed to be his Iraqi fiancee were found by the U.S. military in a grave in September 2008.

The Islamic Army in Iraq claimed in December 2005 that it had killed the pair.

Also Saturday, the U.S. military said an American soldier died Friday in a noncombat incident in Baghdad province.

A military statement said the incident was under investigation. No further details were provided. The name of the soldier has not been released pending notification of next of kin.

At least 4,300 members of the U.S. military have died in the Iraq war, according to an Associated Press count.

The figure includes eight military civilians killed in action. At least 3,443 military personnel died as a result of hostile action, according to the military's numbers.