KABUL, Afghanistan — Insurgents shot down a U.S. helicopter after exchanging fire with its crew in central Afghanistan on Monday, while a suicide bomber in the north killed two American soldiers inside a police station, officials said.

The crew of the helicopter, forced down in a province neighboring Kabul, were rescued and troops were "in the process of recovering" the aircraft," said Lt. Cmdr. Walter Matthew, a U.S. military spokesman.

"The helicopter crew exchanged fire with the enemy before the damage brought the helicopter down," Matthews said.

At least four militants were killed in the exchange, said Fazel Karim Muslim, the chief of Sayed Abad district.

Wardak province has seen an increase in insurgent activity the last two years, and its main highway is now extremely risky to travel on, particularly at night. In mid-October, a U.S. Special Forces raid freed a kidnapped American working for the Army Corps of Engineers who had been held by his captors in Wardak for two months.

The U.S. and other foreign forces rely heavily on helicopters for transportation around Afghanistan, which is covered by rough mountains and long stretches of desert and has few decent roads. Insurgents rarely bring down military helicopters, though they have hit several in recent years.

Separately, a suicide bomber wearing a police uniform blew himself up inside a police station in northern Afghanistan on Monday, killing two American soldiers and wounding five other people, officials said.

The bomber entered a police station in Pul-e-Khumri, the capital of Baghlan province, while Afghan officials were meeting with U.S. troops advising a police training program, provincial police chief Gen. Abdul Rahman Sayed Kheil said.

The blast killed two American soldiers, a U.S. military spokesman said.

Four Afghan security officers were wounded, Kheil said.

It was not immediately clear if the bomber was a policeman or just wearing the police uniform.

Zabiullah Mujahid, a Taliban spokesman, claimed responsibility for the blast in a phone call to an Associated Press reporter. Mujahid said the bomber's name was Abdul Had and that he was from Baghlan province.

Militants in Afghanistan have in the past disguised themselves in police or army uniforms when attacking Afghan and foreign troops. But actual policemen in the Afghan force were responsible for at least two recent attacks in eastern Afghanistan in which two U.S. soldiers died after police opened fire on them in two separate incidents.

More U.S. and NATO troops have died this year in Afghanistan than any other year since the 2001 U.S. invasion, in part because Taliban militants are launching increasingly complex and deadly attacks.

But NATO's top commander in Afghanistan, U.S. Gen. David McKiernan, said he is tired of negative headlines and what he sees as a wave of unwarranted pessimism in news reports.

"Somebody likes to report an attack somewhere and that becomes the trend in Afghanistan, or they don't report the positive events or the absolute brutality or the illegitimacy of the Taliban," McKiernan told The Associated Press in an interview Sunday.

McKiernan highlighted an event last week witnessed by NATO troops in Farah province in which insurgents planting a roadside bomb grabbed two children and used them as human shields when they were attacked by NATO forces.

The four-star general also pointed to a protest last week by about 1,000 Afghans in Laghman province over the slaying of 26 local workers by Taliban militants who stopped a bus in Kandahar and killed many on board.

"That's a rejection of the brutality of the Taliban by the people of Afghanistan, and that needs to be heard," McKiernan said.

"What happens sometimes in reporting is that there's this idea that the Taliban is at the gates of Kabul, or after Sarposa (a massive June prison break) they're about ready to take control of Kandahar, or they're resurgent in Uruzgan or Helmand, and it's just not true," he said.

McKiernan, who took command of the NATO mission in Afghanistan in June, has acknowledged that the country lacks security and governance in many regions but concluded in a recent news conference that "we are not losing Afghanistan."