Fourteen US soldiers were killed in a helicopter crash overnight in northern Iraq, the US military has said.

The Black Hawk helicopter, carrying 10 soldiers and four crew members, crashed after experiencing a mechanical malfunction, a US statement said.

There were reportedly no indications of hostile fire, but the cause of the crash is still under investigation.

Later, at least 15 people died when a suicide bomber drove a fuel tanker into a police station in Baiji, police said.

The head of the local hospital in the oil city, 180km (110 miles) north of Baghdad, said both police and civilians were among the victims. At least 40 people were wounded.

The police had only just moved into the building after a similar attack in June destroyed the old station and killed at least 10 people.

The 14 soldiers killed on Wednesday were part of Task Force Lightning, a US division responsible for a large area of northern Iraq, including the cities of Balad, Kirkuk, Tikrit, Mosul and Samarra.

A second Black Hawk helicopter had been flying alongside them at the time.

It is not known precisely where the helicopter crashed.

It was the deadliest such crash since January, when another Black Hawk went down in Diyala province.

The worst US helicopter crash in Iraq was in January 2005, when 30 marines and a sailor were killed when a Super Stallion came down in bad weather near the Jordanian border.

The BBC's Mike Wooldridge in Baghdad says the fairly frequent losses of helicopters over the past four years has demonstrated the dependence of US forces on them and their vulnerability.

PHOTO CAPTION

In a file photo a UH-60 Blackhawk helicopter lands to extract members of a U.S. Army Combat Team, during a mission near Tall Afar, Iraq, on Monday, June 5, 2006. (AP)

BBC