Oček notified Prime Minister Miro Cerar of the decision on Friday, the Government Communication Office said in a press release on Monday.

In his letter of resignation, Oček said the pressure had begun with his appointment and "affected the implementation of basic tasks in protection of national interests and providing national security".

He decided for resignation in order to "protect the agency and its staff", the release said.

Appointed by the government on 22 October, Oček was described in the media as a low-key SOVA employee who joined the service some 15 years ago. Reports alleged that he was a close family friend of the prime minister's.

Doubts were also raised about his suitability for the post with Vinko Gorenak, an MP for the opposition Democratic Party (SDS) who had served as interior minister in the past, arguing Oček did not meet the requirements for the job.