A Defense Department statement in Washington gave the casualty figure, but it did not say whether the dead and wounded were U.S. soldiers or Iraqis.
The Pentagon said the noontime attack was carried out with rockets and mortars.
The Al-Qaeda-linked Army of Ansar al-Sunna group later claimed responsibility for the attack, in a statement attributed to it on an Islamist website. Its authenticity could not be immediately confirmed.
Mosul, Iraq's third largest city, has seen a wave of recent violence as U.S. forces concentrated on recapturing the central city of Al-Fallujah.Blair Visit
The incident in Mosul comes as British Prime Minister Tony Blair flew into Baghdad today in a surprise visit designed to boost prospects for Iraqi elections in January.
Blair flew in a U.S. military helicopter from Baghdad airport to the central Green Zone, the secure area where the interim Iraqi government has it as administrative offices.
At a news conference with interim Prime Minister Iyad Allawi, Blair said there is no question of running away from the insurgents:
"The danger that people feel here is coming from terrorists and insurgents who are trying to destroy the possibility of this country becoming a democracy," Blair said. "Now, where do we stand in that fight? We stand on the side of the democrats, against the terrorists."
Blair, on his first visit to Baghdad, said those behind the violence are a minority. And he praised the courage of the Iraqi officials working for the government at a difficult time.
"When I meet the people working alongside the United Nations, Iraqis in fear of their life every day because they are trying to bring freedom and democracy to their people -- when I see their courage and their determination and know that they speak for the vast majority of people in Iraq who want that democracy and freedom, then I know that we are doing the right thing," Blair said.
Blair and Allawi both said the elections scheduled for 30 January would go ahead as planned, despite an upsurge in bloodshed that included the killing of three Iraqi Election Commission officials on 19 December and twin suicide car bombings that killed 66 people yesterday.
Allawi said the polls should be open to all Iraqis.
"We look forward for this election to be inclusive," Allawi said. "All Iraqis should participate in this election, and whoever is not going to have the chance, the doors will be open for everyone to be included in the political process as we move steadily in establishing the rule of law, human rights, and the constitution for Iraq."
Blair also met with top U.S. officials. And he was widely expected to visit British troops in the southern city of Al-Basrah before leaving for Israel to promote new peace initiatives.
In other developments, a member of the governing council in Diyala Province, Taleb Ibrahim, was shot dead in the northern city of Baquba.
In Baghdad, interim Interior Minister Falah al-Naqib said 1,000 policemen have been killed since the U.S.-led coalition reestablished Iraq's security forces.
(news agencies)For more on events in Iraq, see RFE/RL's dedicated The New Iraq webpage.