Members of the churches, one Armenian, the other Chaldean, said gunmen burst in, forced people to leave and set off explosions inside the buildings, damaging them but hurting no one.
Smoke poured from the Armenian church and flames could be seen inside the Chaldean church, Reuters reporters said. It was not clear how many people had been in the churches when they were attacked but the number was apparently not large.
Mosul, population 1.2 million, is home to many of Iraq’s Christians, who make up about three percent of the national population.
Tension between Mosul’s two main Sunni Muslim communities, Arabs and Kurds, has been high since Arab guerrillas routed the city’s U.S.-trained police last month. U.S. forces have brought in Kurdish units to keep order.
At least 16 Kurdish peshmerga fighters were killed in a suicide car bomb attack in Mosul on Saturday.
Christians have been attacked several times in the past few months.
Coordinated car bombings in Baghdad and Mosul killed at least 12 people in August and five Baghdad churches were bombed on Oct. 16 at the start of the Muslim holy month of Ramadan.
At least eight people were killed in two church bombings in the capital on Nov. 8, and a car bomber attacked police guarding the hospital where the wounded had been taken.
Figures are not available but some of Iraq’s estimated 650,000 Christians, mostly Chaldeans, Assyrians and Catholics, have left since the fall of Saddam Hussein or are contemplating leaving the country.
Some have been involved in businesses such as selling liquor and have fallen foul of radical Muslims opposed to such trade.