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Fort Hood commanders were in the process of closing roads on the sprawling Army post in Central Texas when a truck carrying 12 soldiers overturned in a fast-flowing flooded creek during a training exercise, killing five and leaving four missing, officials said Friday.

The portion of road on the northern fringe of the post where the Light Medium Tactical Vehicle overturned Thursday hadn't been overrun by water during past floods, Fort Hood spokesman Chris Haug said. The vehicle resembles a flatbed truck with a walled bed and is used to carry troops.

He said during a news conference Friday that the soldiers were being trained on how to operate the 2 ½-ton truck when it overturned along Owl Creek, about 70 miles north of Austin.

"It was a situation where the rain had come, the water was rising quickly and we were in the process, at the moment of the event, of closing the roads," Haug said.

Soldiers on training exercises regularly contend with high-water situations following heavy rains, he said.

"This was a tactical vehicle and at the time they were in a proper place for what they were training," Haug said. "It's just an unfortunate accident that occurred quickly."

The bodies of two soldiers were found late Thursday night. Three soldiers were found dead shortly after the vehicle overturned. Three others were rescued by personnel traveling in a separate vehicle and hospitalized in stable condition.

Aerial and ground crews Friday were searching the 20-mile creek that winds through heavily wooded terrain. Army aircraft, canine search teams, swift-water rescue watercraft and heavy trucks were being used.

The Army has not yet released the names of the dead because it's still notifying relatives.

Maj. Gen. John Uberti said the three injured soldiers could be released from a post hospital later Friday.

"This tragedy extends well beyond Fort Hood and the outpouring of support from the country is sincerely appreciated," he said.

Parts of Texas have been inundated with rain in the last week, and more than half of the state is under flood watches or warnings, including the counties near Fort Hood. At least six people died in floods last week in Central and Southeast Texas.

Gov. Greg Abbott issued a statement saying the state "stands ready to provide any assistance to Fort Hood as they deal with this tragedy."

The base has seen fatal training accidents before. In November 2015, four soldiers were killed when a Black Hawk helicopter crashed during a training exercise. And in June 2007, a soldier who went missing for four days after a solo navigation exercise died from hyperthermia and dehydration while training in 90-degree heat.

Thursday's accident came the same day the Navy said a pilot was killed when his Blue Angels fighter jet crashed near Nashville. Speaking in Singapore, U.S. Defense Secretary Ash Carter expressed condolences to the families of those killed in both accidents and said once investigations are complete, the military will take actions designed to prevent such incidents in the future.

Also Thursday, the pilot of a U.S. Air Force Thunderbird ejected safely into a Colorado field, crashing the fighter jet moments after flying over a crowd watching President Barack Obama's commencement address for Air Force cadets.

Across Texas, a new batch of storms brought more rain, worsening flooding caused by waterways that already have risen to record levels.

The heaviest rainfall Thursday night was reported in LaPorte, on the western shore of Galveston Bay, where 4.36 inches of rain was recorded between 5 p.m. and 8 p.m.

A storm system overnight Wednesday dumped nearly 8 inches of rain on Houston's northern suburbs, flooding some neighborhoods. In Fort Bend County, southwest of Houston, about 1,400 homes have been affected by the Brazos River, swollen by heavy rainfall from last week.

Officials say the Brazos has not dropped much and that additional rainfall could make the flooding worse.

"With the rain that's predicted, that's not going to help things as that water has no place to go," said Lt. Lowell Neinast, with the police department in Richmond, where more than 700 people have been evacuated from their homes.

This week's storms are the latest in a string of torrential rains since May 2015 that have put swaths of the state under water. Some areas now overwhelmed by water had run dry two years ago due to drought conditions.

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Associated Press writers Terry Wallace in Dallas and Juan Lozano in Houston contributed to this report.