Chicago (AFP) - Police quickly apprehended a 46-year-old white male in the shooting death of two police officers who were "ambushed" in separate attacks in the US state of Iowa early Wednesday, authorities said.

Scott Michael Greene from Urbandale -- a suburb of state capital Des Moines -- was captured less than two hours after police released his name and said they were searching for him. They had cautioned that Greene should be considered armed and dangerous.

"We think he's got some information that's pretty critical to us closing this case out. We can't go into great detail right now. But, he's definitely somebody that we want to talk to," Des Moines Police Sergeant Paul Parizek said in an early morning news conference.

Police said two officers were "ambushed" in the early morning hours Wednesday, with footage of one of their police cars showing bullet holes on the front passenger side door.

"It doesn't look like there was any interaction between these officers, and whoever the coward is... shot them as they sat in their cars," Parizek said.

For more news videos visit Yahoo View, available now on iOS.

Authorities said a member of the Urbandale police force was found dead just after 1:00 am (0600 GMT).

Twenty minutes later, a second Des Moines police officer was discovered gunned down at an intersection around two miles away. US media said the officer died after being taken to the hospital.

Parizek told reporters police would be doubling up to patrol in pairs in the wake of the shootings.

"There is a clear and present danger to police officers right now and we've doubled up our police officers" so that no one is working alone, he said.

A series of tips and leads drew investigators to Greene, the officers said, although they declined to comment on a motive for the killings.

"I think you know that oftentimes in these investigations we don't figure out what the motive is until we get done and then there's times we can't make sense of what their motive is, or they don't even share that with us," Parizek said.

Story continues

The incident marks the first time a Des Moines officer has been shot in the line of duty since two police were gunned down in 1977, The Des Moines Register said.

The United States was on edge for weeks in July following the shooting in Dallas of five officers and a similar assault in Baton Rouge, Louisiana, where three officers were shot dead by a former military veteran.

Those killings were carried out in apparent retribution for a string of high-profile police shootings of black citizens which inflamed racial tensions in the United States.