The AP identified the victims as Associated Press Television News cameraman Saleh Ibrahim and photographer Mohamed Ibrahim, no relation to the deceased. Saleh Ibrahim was in his early 30s and was a father of five.
The circumstances of the death and injury remain unclear.
The explosion happened at about 2.30pm local time near the al-Yarmuk roundabout in the city 350km north of Baghdad, according to other journalists who responded to the blast.
The cause of the explosion was also not immediately determined.
The two AP journalists drove to the scene together, according to a colleague who was at the scene as well. US forces were in the area when they arrived, the colleague said.
Gunfire broke out, and Saleh Ibrahim and Mohamed Ibrahim were hit, the colleague said. The colleague's employer asked that his name not be used because of fear for his safety.
Colonel Wathiq Ali, the deputy police chief in Mosul, said the explosion targeted a US patrol and injured two Iraqi civilians.
"The police did not interfere in that incident because the US troops were there," he said.
The colleague drove the two injured AP journalists to the al-Jumhuri Educational Hospital. Saleh Ibrahim was treated for three bullet wounds to the chest and died soon after arrival, Dr Rabai Yassin said at the hospital.
Mohamed Ibrahim was treated for shrapnel wounds to the back of the head, Yassin said.
While at the hospital, Mohamed Ibrahim was escorted away by US forces and his whereabouts could not immediately be determined.
Reporters in Iraq have been
killed, injured and kidnapped
The US military said it was investigating.
Saleh Ibrahim was the 28th journalist to be killed while on assignment since the AP news cooperative was founded in 1848.
In addition, Ismail Tahir Muhsin, an Iraqi driver who worked for the AP, was ambushed by gunmen and killed near his home in Baghdad last September. The reasons for the slaying have never become clear.