Image caption The suspected gunman is said to have run through creeks to shake off trackers

Police are scouring a national park in Washington state for an Iraq war veteran wanted in connection with the killing of a ranger.

Mount Rainier National Park has been closed since Margaret Anderson, 34, was shot dead while trying to stop a vehicle on Sunday morning.

The suspected gunman, Benjamin Colton Barnes, 24, has also been linked to an earlier shooting at a New Year's party.

The US Marine is reported to have post-traumatic stress disorder.

Police said they had recovered his vehicle, which had weapons, body armour and survivalist gear inside.

The gunman sped past a park checkpoint that was monitoring if vehicles had tyre chains, sometimes required in snowy conditions.

'Argument over weapon'

As one ranger gave chase, mother-of-two Mrs Anderson blocked the road with her vehicle to stop the driver.

Both of them were fired on, but only Mrs Anderson, who was married to another ranger, was hit.

Image caption Margaret Anderson was married and had two young children

Response teams could not reach the wounded officer for nearly an hour-and-a-half because the gunman continued to shoot, the Seattle Times newspaper quotes officials as saying.

Police said Mr Barnes was already wanted for questioning over an early-morning shooting at a party in Skyway, just south of Seattle, which left four people injured, two critically.

Witnesses said a number of revellers at the gathering had been armed and that gunfire broke out following an argument over a weapon.

The national park shooting happened as hikers and climbers enjoyed the wooded trails and views of the 14,410 ft (4,392m) Mount Rainier on an unseasonably mild New Year's holiday.

The park was immediately closed, and about 125 visitors were moved into a visitors' centre before being evacuated under cover of darkness on Monday morning.

One visitor, Dinh Jackson of Olympia, Washington, told the Associated Press news agency that officials had ordered everyone to kneel and place their hands behind their heads as they searched the crowd to check the suspect was not among them.

"That was scary for the kids," she said.

'Angry and depressed'

An aircraft fitted with heat-sensing technology has been helping to search for the suspect from the air, while 150 officers combed the park's grounds.

Pierce County Sheriff's spokesman Ed Troyer said the ongoing search was "a very hot and dangerous situation" with teams of tactical responders pursuing the gunman's tracks in the snow.

Mr Troyer added that the gunman had run through creeks, which made it harder to follow his tracks.

The gunman is said to have been suicidal and was possibly suffering from post-traumatic stress disorder following his deployments to Iraq in 2007-08, according to an affidavit submitted by the mother of his child.

She sought a temporary restraining order against Mr Barnes during a custody dispute in July 2011.

Mr Barnes gets easily irritated, angry and depressed, she added, saying he keeps a variety of weapons in his home.

Park superintendent Randy King said of Mrs Anderson's death: "It's just a huge tragedy - for the family, the park and the park service."

The park will remain closed on Monday while the search continues through its 368 sq miles (953 sq km) of terrain.