Updated

A U.S. Air Force F-16 fighter jet crashed Friday during a close air support mission for ground forces in Iraq — a rare loss of the workhorse aircraft. Meanwhile, Defense Secretary Robert Gates came to Baghdad on an unannounced visit, and the U.S. military said five soldiers had died.

An Air Force announcement, which referred to the 12:27 a.m. crash of the F-16 as an accident, did not say where it occurred or what happened to the pilot, the single crew member. It said the military was investigating the cause of the crash.

An Ohio National Guard spokesman said the pilot, whom he did not identify, was a member of the 180th Fighter Wing based in Toledo. Spokesman Mark Wayda said about 270 of the unit's 1,000 members were deployed to Iraq last month. The jet was operating under the 332nd Air Expeditionary Wing at Balad Air Base, 50 miles north of Baghdad.

The loss of an F-16 is an uncommon event. One crashed last Nov. 27 in the western province of Anbar, killing the pilot.

Speaking to reporters on the flight to Baghdad, Gates said the military wasn't trying to paint an overly optimistic picture of how the war is going.

"It's a very mixed picture," he said when asked whether the military and commanding Gen. David Petraeus were offering realistic assessments of the violence in Baghdad. Since Feb. 14, the military has sent nearly 30,000 more soldiers to Iraq, most of them to Baghdad.

"I have every confidence in General Petraeus and in his ability and willingness to call it as he sees it," Gates said.

Three of the U.S. soldiers, whose deaths were reported Friday by the military, died when a bomb exploded near their vehicle Thursday during operations in Kirkuk province, in northern Iraq. Another soldier was wounded in the blast.

A fourth soldier was killed by small-arms fire the same day in Diyala province, northeast of Baghdad. And another soldier died Wednesday in a non-combat related incident.

All were assigned to Task Force Lightning, and their names were withheld until their families could be notified.

In the deep south of Iraq, police said bombers posing as television cameramen destroyed an important Sunni shrine, and Prime Minister Nouri al-Maliki ordered an indefinite curfew in Basra, Iraq's second-largest city.

The attack on the Talha Bin al-Zubair shrine, 13 miles outside Basra, appeared to be the work of Shiite militants who were seeking revenge for Wednesday's provocative attack on the al-Askariya Shiite shrine that brought down its golden minarets in Samarra, 50 miles north of the capital.

In February 2006, suspected Al Qaeda bombers blew up the al-Askariya mosque's glistening golden dome. That attack set in motion the sectarian slaughter that has shredded the fabric of Iraqi society and killed tens of thousands of Iraqis.

To prevent such widescale violence from happening again, al-Maliki extended a vehicle ban in Baghdad for one more day, again keeping the capital relatively quiet. There were 16 reported violent deaths nationwide on Friday, one of them a body dumped in Baghdad. Daily totals of death squad victims in Baghdad have been running well above 20.

Photographs of the shrine near Basra showed that the big structure was leveled, a result that would have required huge amounts of explosives — more than even several men could have carried into the mosque concealed in television equipment bags. Militants had first hit the al-Zubair shrine with rocket-propelled grenades Thursday night.

According to Gen. Ali al-Mussawi, a top Basra security official, a group of men posing as television cameramen went to the mosque Friday morning and asked guards if they could film inside the shrine. They instead planted bombs inside the structure and demolished it, he said. There were no reported casualties.

The guards were detained afterward for questioning, al-Mussawi said.

Al-Maliki's office issued a statement that called the bombing of the Sunni shrine another of the "crimes aimed at sowing sedition and inflaming sectarian strife among the people."

In Tehran, Iran's supreme leader, Ayatollah Ali Khamenei, accused U.S.-led forces in Iraq of plotting and extremist Sunni groups of carrying out Wednesday's attack on the shrine in Samarra, saying it was designed to provoke civil war. The Shiite majority in Iraq has deep ties to Iran and many top Iraqi politicians spent long periods in Iranian exile during Saddam Hussein's reign.

Separately, an Iranian Foreign Ministry spokesman said Friday that U.S. forces detained and interrogated three Iranian diplomats in Iraq, the official news agency in Tehran reported.

Mohammad Ali Hosseini, the spokesman, condemned the detentions, which he said occurred while the diplomats were traveling from Iraq to Iran on Friday to spend the weekend at home.

The three were first detained by Iraqi police, then later held by U.S. troops and questioned for several hours, Hosseini said, stressing that Iraqi authorities had been informed in advance of the diplomats' travel plans. The diplomats were later handed back to Iraqi police who took them to the Iranian Embassy in Baghdad, Hosseini said.

U.S. officials in Baghdad did not immediately comment on the claim of the Friday detentions.

But Iraqi government spokesman Ali al-Dabbagh confirmed most of the details in the Iranian Foreign Ministry account, saying the diplomats were headed to the Iranian border when they were intercepted by an Iraqi police patrol in southeast Baghdad.

Al-Dabbagh said they were briefly questioned and allowed to continue, but they were later detained by a U.S. military patrol. He told The Associated Press that the Americans later released the three men.

Detentions of Iranian nationals have led to increased tensions between Washington and Tehran since U.S. troops in January arrested five Iranians in the northern city of Irbil.

The U.S. military has said the five, who remain in U.S. custody, are suspected of links to a network supplying arms to Iraqi insurgents — an accusation denied by Iran which maintains they are diplomats.

Iran, meanwhile, has detained four Iranian-American scholars and activists charged with acting against Iranian national security.