Angela Merkel and Gordon Brown held a joint press conference in Berlin
German Chancellor Angela Merkel has called for an urgent investigation into an airstrike in northern Afghanistan, amid tension about who was to blame.
Reports have suggested that civilians were among the dozens of victims of Friday's German-ordered air strike.
The Kunduz province raid has strained relations between German and US commanders in Afghanistan.
Meanwhile, three members of one family have died in a rocket attack in the Afghan capital Kabul.
Two other people were injured when the rocket fired early on Monday by insurgents landed on a house in a western suburb of the city, an interior ministry official said.
In Sunday's joint announcement in Berlin with UK Prime Minister Gordon Brown, Ms Merkel also said a major summit on Afghanistan should be held this year.
Germany has 4,200 troops in Afghanistan
The British and German leaders said the meeting should focus on helping Afghanistan take on more responsibility.
The BBC's Steve Rosenberg in Berlin says the politicians are concerned about the urgent need for an Afghan exit strategy.
Friday's airstrike - called in after Taliban rebels hijacked two fuel tankers - has caused uproar in Germany, which will hold parliamentary elections on 27 September.
Speaking in Berlin on Sunday, Ms Merkel said if any civilians died in the air strike, she would "naturally deeply regret that".
"The German government and I personally want to see a Nato investigative team swiftly put together that will carry out a thorough and quick explanation of what took place," she said.
Her comments came as the Washington Post reported that the strike may have been ordered in breach of Nato rules.
The German commander reportedly called in the raid after seeing live footage of the tankers, with people around them, beamed from US aircraft in the skies above Kunduz.
The footage would have been grainy, US spokesman Rear Adm Gregory Smith told the Associated Press news agency.
Latest poll results
The Germans, who also spoke to an informant at the scene, decided the people were militants.
German Defence Minister Franz Josef Jung said "it was clear our soldiers were in danger".
The Washington Post reported that using a single human source for intelligence appeared to breach guidelines aimed at reducing civilian deaths.
Nato has said the investigation into what happened is still ongoing.
Also on Sunday the latest partial results from last month's Afghanistan's presidential election showed incumbent Hamid Karzai within touching distance of the 50% threshold needed to avoid a run-off ballot.
With three-quarters of votes counted, he had 48.6%, followed by Abdullah Abdullah with 31.7%.
Meanwhile, a Swedish charity has alleged foreign troops entered its hospital south of the Afghan capital Kabul, smashed doors and tied up staff and patients' relatives.
The Swedish Committee for Afghanistan said the soldiers came into the clinic in Shaniz in Wardak province late on Wednesday "without giving any reason or justification".
An Isaf spokesman said an investigation had been launched.