* USAF helicopter crashes in rural England
* All crew thought to have been killed, say police
* Sikorsky Pave Hawk was on training exercise
By Michael Holden
LONDON, Jan 7 (Reuters) - Four crew on board a U.S. military helicopter were killed when their aircraft crashed in eastern England during a routine training operation on Tuesday, police and U.S. Air Force (USAF)officials said.
The helicopter, assigned to the 48th Fighter Wing based at the nearby U.S. air base RAF Lakenheath, went down at about 1800 GMT on marshland on the north Norfolk coast, a rural area about 130 miles (209 km) northeast of London.
"We can confirm that one of our HH-60G Pave Hawk helicopters went down outside Cley during a low-level flying exercise," said a spokesman at the USAF base. "The conditions of the four crew members are unknown at this time."
Norfolk Police said in a statement that the helicopter's four occupants were thought to have died in the crash.
"Sadly we believe that at this time all four of the crew are deceased," Superintendent Roger Wilson of Norfolk Police told reporters.
Police said next of kin would be informed before further details on the victims were released.
There was no immediate information as to the cause of the crash. The Pave Hawk is made by Sikorsky Aircraft Co, a unit of United Technologies Corp.
Police said a 400 metre (quarter-mile) area had been cordoned off at the crash site, a nature reserve, while it was determined from the U.S. military what munitions the helicopter was carrying at the time.
However, no one in the surrounding area had been in any danger, Wilson said.
The U.S. Air Force website said the primary mission of the Pave Hawk helicopter, a highly modified version of the Army Black Hawk, was "to conduct day or night operations into hostile environments to recover downed aircrew or other isolated personnel during war."
It added each aircraft had an automatic flight control system, night vision goggles and a forward looking infrared system "that greatly enhances night low-level operations", along with anti-ice features to cope with adverse weather.
Lakenheath is also home to Europe's only F-15 fighter wing, and local media reported that F-15 planes had been flying over the crash site.
In 2001, two single-seat F-15Cs from Lakenheath crashed while on a low-flying training mission over Scotland, killing both pilots.