German authorities are investigating the second case of a government employee suspected of spying on confidential government affairs for US secret services within a week.

Public prosecutors confirmed that the home and office of a defence ministry employee in the greater Berlin area had been searched on Wednesday morning.

They told the Guardian that a search had been conducted "under suspicion of secret agent activity" and that evidence – including computers and several data storage devices – had been seized for analysis. The federal prosecutor's office confirmed that no arrest had yet been made.

According to Die Welt newspaper, the staffer being investigated is a soldier who had caught the attention of the German military counter-intelligence service after establishing regular contact with people thought to be working for a US secret agency.

The news came just days after a member of the German intelligence agency BND confessed to having passed more than 200 confidential files to a contact at the CIA.

The new case is not thought to be directly related to that of the BND staffer. However, one government insider familiar with the case told Süddeutsche Zeitung that the new case being investigated was "more serious" than that of the BND spy, in which the sold documents are thought to have been of limited value.

Last week's spying scandal gave a detailed picture of how US security agencies manage to recruit foreign agents. The staffer, employed at the German intelligence agency's department for foreign deployments, had managed to establish contact with the CIA after emailing the US embassy in Germany.

At a meeting in a Salzburg hotel, the CIA then equipped the BND employee with a specially encrypted laptop, which allowed the agent to keep in touch with the US secret service on a weekly basis: every time he opened a programme disguised as a weather app, a direct connection was established with a contact in America.

The BND employee, who is said to have a physical disability and a speech impediment, received around 25,000 euros (£20,000) for 218 confidential documents, though sources within the intelligence service told German newspapers that the 31-year-old had been motivated less by financial interests than by a craving for recognition.

After the CIA had apparently lost interest in him, he had offered his services to the Russian general consulate in Munich, inadvertently catching the attention of the German counter-espionage agency.

The Social Democratic party has reacted to the succession of scandals by urging the US to stop all of its espionage activity within Germany. Thomas Oppermann, the head of the SPD parliamentary group, told Der Spiegel: "It is a degrading spectacle to watch US spies being exposed on a weekly basis." The politician warned that trust in America's alliance with Germany could "collapse completely".

US officials have been trying to limit the diplomatic fallout, with the CIA's head, John Brennan, reportedly calling Angela Merkel, the German chancellor, in the wake of the latest spying scandal.

Over the course of the last week, the US ambassador in Berlin has twice had to visit the German foreign ministry to explain his position on the matter. After being called in for an initial meeting last Friday, John Emerson returned to the ministry for a second meeting with a senior official on Wednesday.

In a speech on Tuesday, Emerson acknowledged that "we must acknowledge that the German-American relationship is now undergoing a difficult challenge".