In the first incident, a US soldier was shot dead with a member of the Patriotic Union of Kurdista(PUK) in a drive-by shooting, the US military said.
A second US soldier was wounded and a resistance fighter was also killed, the military said.
Another American soldier was killed and three injured when a roadside bomb hit their convoy.
The incidents occurred just one day after an explosive-laden car was detonated near US troops near Mosul, leaving up to 60 soldiers wounded.
Since US President George Bush declared an end to hostilities on 1 May, more than 194 soldiers have been killed in resistance attacks.
Also, a US Apache helicopter made a "controlled landing" south of Mosul after a fire broke out on board, said a military spokesman.
The spokesman said he had no information on whether the
helicopter had come under fire from resistance fighters. There were no reports of any casualties.
On Tuesday, a US Kiowa helicopter also made a "controlled hard landing" near the flashpoint town of Falluja, west of Baghdad, after coming under ground fire. The two-man crew escaped injury.
Underfire: A Kiowa helicopter
made a hard landing near Falluja
Last month, fighters shot down three US Black Hawks and
one Chinook in Iraq, killing 39 American soldiers.
Also on Tuesday, a US Air Force C-17 transport aircraft was hit by a missile as it took off from Baghdad. However, it landed back safely and only one person was slightly injured, said a US official speaking on condition of anonymity.
It is believed to be only the second time a plane has been hit by a surface-to-air missile since the end of major combat.
The official said the incident was similar to the first on
22 November when a DHL cargo plane was hit by a shoulder fired SA-14 as it was taking off from Baghdad airport.
DHL resumed flights into Iraq on 3 December.
In another development, hundreds of Iraqis, watched over by US Apache helicopters, demonstrated on Wednesday to condemn what they said was "terrorism" in their country.
More than 200 protesters from the Iraqi National Congress and other political parties, women's groups and shaikhs gathered near the National Theatre.
Similar rallies will be held to mark
international Human Rights Day
As more demonstrators arrived, they said they would march outside a central Baghdad hotel.
Participants said similar rallies would be held in other major
Iraqi cities to mark the international Human Rights Day. A similar protest last Friday in the capital attracted about 1000 Iraqis.