US Secretary of State Condoleezza Rice has met German Chancellor Angela Merkel for talks dominated by reports that CIA planes flew terror suspects via Europe.
Mrs Merkel is keen to improve relations with the US
Mrs Merkel told a joint news conference that democratic rules should be adhered to, but added that intelligence services must be able to do their job.
Ms Rice reiterated that the US does not carry out or condone torture.
The CIA flights and reports that the US spy agency ran secret prisons in Europe is set to dominate Ms Rice's tour.
Her next stop, Romania, is one of the countries that human rights activists believe housed a CIA secret prison - a charge the Romanian government denies.
Ms Rice has refused to address claims of secret prisons where suspects are said to have been interrogated without reference to international law.
In Berlin, Ms Rice and Mrs Merkel sought to dampen down the discussion about alleged CIA practices, the BBC's Ray Furlong reports.
Mrs Merkel said Ms Rice had given "important" reassurances that the US would use "every lawful means" to protect citizens from the threat of international terrorism.
Ms Rice said the US respected the sovereignty of its partners, adding that the US had an obligation to defend its people and would use every lawful means to do so.
"We will live up, in the United States, to our commitments under our laws, and to our international obligations," she said.
'Form of kidnapping'
The new German chancellor came to power pledging to improve links with Washington and emphasising the importance of the war on terror.
Ms Rice's trip, which will also take in Kiev and Brussels, follows claims from Germany that it has a list of more than 400 CIA flights and landings on its territory.
Before she left the US, Ms Rice admitted that terror suspects were flown abroad for interrogation but denied they were tortured.
She said suspects were moved by plane under a process known as rendition, and that this was "a lawful weapon".
A leading US-based human rights group accused Ms Rice of seeking to "mischaracterise" the true nature of rendition.
"Secretary Rice made extra-legal rendition sound like just another form of extradition," said Tom Malinowski, a Human Rights Watch official in Washington.
"In fact, it's a form of kidnapping and 'disappearing' someone entirely outside the law."
The controversy surrounding claims of covert CIA operations on foreign soil has been swirling for weeks.
In Germany, it has been alleged that some German officials knew about the secret flights.
According to media reports, former German Interior Minister Otto Schily was informed last year by the US about a German citizen seized in Macedonia and then flown to a prison in Afghanistan, where he was kept for five months.
Mr Schily has not commented and the ministry says it is investigating.
Meanwhile, ABC News claims the CIA moved 11 top al-Qaeda suspects from prisons in eastern Europe to a new facility in North Africa last month.
Current and former CIA members reportedly told the US channel the move was carried out hurriedly ahead of Ms Rice's visit to Europe.