Officers were shot at a checkpoint on the road to Qassim province after ordering a car to stop. The attackers fled in two stolen police cars.

Police said the men had probably been involved in a gun battle in Riyadh on Monday in which one suspected militant and one police officer died.

Police also defused two car bombs and seized a third car full of arms.

The cars were discovered by police helicopters in a desert region not far from the scene of the shooting at Um Sedra checkpoint.

"The terrorists had packed a huge quantity of explosives in the cars and they would have caused major damage," a security source told Reuters.

The gunmen were chased to a suburb of the city of Unaizah, south of Qassim province. Police have cordoned off an area of the city and are conducting searches.

A statement from the Interior Ministry said the latest attacks were carried out by members of a "deviant minority".

The BBC's Kim Ghattas in Riyadh says this is how authorities often refer to suspected Islamist sympathisers of al-Qaeda, describing them as Muslims who have strayed from the right path.

Terror list

Following the latest incidents, the US embassy in Riyadh has updated its security message to US citizens in the kingdom, urging them to remain vigilant.

More than 50 people were killed last year in two separate attacks against compounds housing foreigners.

Qassim is the heartland of Saudi Arabia's austere Wahhabi creed and has in the past been used as a hideout by militant fugitives.

In Monday's violence, militants fired rocket-propelled grenades at the police.

This the second violent outbreak in less than two weeks. One militant was killed and another wounded during a shootout in Riyadh last Monday.

In December, the government published the names and pictures of 26 men it suspected of involvement in terror attacks within the country.

So far, three on the list have been killed and one has surrendered.