The need to maintain close ties with Washington while at the same time responding to public outrage over American spying has proven challenging for Merkel, who had sought to play down the allegations when they first surfaced last spring.
That changed, however, with media reports last month that Merkel's own cellphone had been tapped by NSA operatives. The reports unleashed a firestorm of criticism in Germany, threatening one of America's closest political relationships in Europe.
In the wake of those reports, the German government sent delegations to Washington to press for a no-spying pact with the Americans.
Interior Minister Hans-Peter Friedrich told Parliament that the U.S. had not been as forthcoming during those talks as the Germans had hoped.
"The Americans need to come clean," Friedrich said. "They cannot become entangled in contradictions...The silence means there are all sorts of conspiracy theories."
Frank-Walter Steinmeier, a former foreign minister, said Berlin should not be satisfied until it gets "reliable, verifiable agreements" with Washington to prevent future spying.
The steady drumbeat of revelations has focused public attention on the broader issue of America's security role in Germany, where the U.S. still maintains more than 30,000 troops. The reports have questioned whether German sovereignty has been compromised, making it more difficult for Merkel to contain the political damage.
The Sueddeutsche Zeitung newspaper has reported the U.S. is directing drone attacks in Africa from bases in Germany. The newspaper has also reported that more than 50 U.S. agents based at German airports and seaports decide who can fly to the U.S. and enjoy diplomatic immunity and power "akin to German customs and police officers."
An Interior Ministry spokeswoman, Mareike Kutt, told reporters that the U.S. agents were dealing with immigration issues and "they are not allowed to make decisions regarding sovereign measures in Germany, such as arrests."