In a separate incident in Baghdad, at least one Iraqi civilian died and 18 others were injured in the blast from a roadside bomb aimed at a passing US military patrol.
The attacks came as the US president, George Bush, held his first meeting in a year with the German chancellor, Gerhard Schröder, in an attempt to bridge their divide over the Iraq conflict.
More than five months after American troops took control of Iraq, it is still gripped by lawlessness and growing violence.
In Mosul, witnesses said several bodies were carried from the cinema, some seriously injured by shrapnel and glass. There were posters in the cinema advertising Italian and German porn movies.
The sudden flood of foreign films into Iraq has raised the ire of religious hardliners. Cinema owners showing pornographic films have been threatened, and in some towns there have been attacks on alcohol factories and shops selling western clothes for women.
In the attack in Baghdad, a roadside bomb exploded close to a US patrol, destroying two Iraqi buses. No troops were hurt, but one Iraqi was killed and at least five of the injured were reported to be a serious condition.
Iraqi officials also warned that a member of the US-appointed governing council who was shot leaving her home last Saturday was in a worsening condition in hospital. Aqila al-Hashimi, one of the three women on the council, suffered serious bullet wounds to her abdomen.
Entifadh Qanbar, a member of the Iraqi national c ongress, which holds a seat on the council, said her condition had "deteriorated dramatically". A senior American official later admitted that Ms al-Hashimi, who has undergone several operations at a US military hospital in Baghdad, had suffered a "serious decline".
In New York, Mr Bush resumed his diplomatic attempt to persuade other countries at the UN to share the burden for policing Iraq. He claimed that he had patched up his differences with Mr Schröder. He had told the German chancellor: "We have had differences and they are over, and we're going to work together."
Mr Schröder, for his part, renewed a German offer to train Iraqi police and security personnel. But Berlin stands steadfast against contributing peacekeeping troops. It opposed the war from the outset.
The meeting failed to bridge the gulf between the two leaders on the pace of transition to a sovereign democracy in Iraq, and the degree of political control the UN should have in the near future.
Mr Schröder said: "Only the United Nations can guarantee the legitimacy that is needed to enable the Iraqi population to rapidly rebuild their country under an independent, representative government."
Germany and France would like to see the handover of power to Iraqis take place within months; Washington has refused to set a timetable.
The US has tabled a resolution in the UN security council calling for a multinational force in the area, but Germany, which has a seat on the council, would like the occupying powers to share power if the international community is going to share responsibility.
Mr Schröder said Mr Bush had spoken "very positively" about the UN's role, adding: 'It should be possible to work out a degree of common ground in the next few weeks that makes it possible to achieve a common resolution."
Mr Bush may find some solace in a new Gallup poll which suggests that most Iraqis in Baghdad believe that ousting Saddam Hussein was worth the troubles that have followed the war. About two-thirds of the 1,178 adults questioned said they believed Iraq would be in a better condition in five years time than it was before the US-led invasion.
But they had mixed views on whether the country was in a worse state now than before the war: 47% said they felt Iraq was worse off.