Norway scrambled to avoid a diplomatic spat with Islamabad on Thursday after a top official inadvertently revealed it had spies operating in Pakistan.
Oslo's ambassador met Pakistani foreign ministry officials to explain comments by internal security chief Janne Kristiansen that Norway, a close U.S. ally, had military intelligence agents in the country.
Kristiansen quit late on Wednesday, hours after revealing the confidential information to an open parliamentary hearing.
Pakistan's Foreign Minister Hina Rabbani Khar told Reuters he wanted more information from Norway's envoy.
"The ambassador has been called to be able to explain whatever is happening, because this seemed like a serious news so we obviously want to get to the bottom of it," he said.
Abdul Basit, a Pakistani foreign ministry spokesman, said earlier that the Norwegian ambassador had already met ministry officials. He gave no details but said Kristiansen's comments had not damaged ties.
"We have a great relationship with Norway with regards to counterterrorism," he said.
NATO member Norway has several hundred troops in Afghanistan, but was not known to have operatives in neighbouring Pakistan.
Kristiansen, who led the PST agency that deals with Norway's internal security, did not say why the agents were there.
"Janne Kristiansen has informed the justice minister that she will resign," the justice ministry said in a statement. "The reason is the possible breach of confidentiality through the disclosure of classified information."
Norway's police said they would investigate possible criminal liability for the breach.
According to a transcript of the parliamentary hearing, Kristiansen was asked if Norway should have contacts with Pakistani intelligence.
She replied that the intelligence agency operated by the armed forces, the E service, already worked in Pakistan.
"The E service has its representatives in these countries, so we cooperate via the E service about this country," she said.
Kristiansen was already under fire at home for missing signs that a far-right extremist was preparing attacks that killed 77 people in July, the worst violence in the Nordic country since World War Two.
She said her agency could not have done more to stop Islamophobe Anders Behring Breivik.
Norway has good diplomatic ties with most countries but fell out with China in 2010 after the Nobel Peace Prize Committee selected Chinese dissident Liu Xiaobo for the prize.
The government may have limited domestic public relations damage with Kristiansen's resignation, as the opposition aimed its criticism at her and not the government.