The Afghan attorney general's office has barred a New York Times reporter from leaving the country after the paper ran a story about ministry and palace officials discussing plans to form an interim government if an election deadlock continues.
Afghanistan is in the midst of a ballot that has dragged on for months, with both candidates claiming victory after the June 14 run off, and allegations of mass fraud threatening to derail the process.
Matthew Rosenberg, who has spent the past three years covering Afghanistan for the Times, was summoned to the attorney general's office for questioning on Tuesday.
"They had brought us there under the guise of a kind of semi informal chat," Rosenberg said. "It was kind of polite but insistent that we give them the names of our sources."
The officials present allowed Rosenberg to leave on the condition he returned with a lawyer the next day. The travel ban was not mentioned at the time and the officials did not name any criminal charge under investigation
"He's not arrested, but he is not allowed to leave until this issue is resolved," attorney general spokesman Basir Azizi told Reuters by telephone.
Azizi said the investigation was expected to take a few days and Rosenberg had been told to return for questioning on Wednesday.
"The report is against our national security because right now, the election problem is ongoing and talks are at a very intricate stage," Azizi said.
Washington criticised the Afghanistan government's handling of the situation.
"We are deeply disturbed by the actions of the Afghan attorney general and by this travel ban that has allegedly been put into place, and urge the Afghan government to respect fundamental freedoms of expression and expression of the press," Marie Harf, a deputy State Department spokeswoman, told a news briefing in Washington on Tuesday.
The United Nations is supervising an audit of all eight million votes cast, but the process has proceeded slowly as rival camps scrutinise each vote.
At the same time, members of a joint-commission appointed by deadlocked candidates Abdullah Abdullah and Ashraf Ghani are meeting to hammer out an agreement on a unity government - as agreed in a deal brokered by US Secretary of State John Kerry, who has twice flown into Kabul since the run off.
While Afghanistan's press has generally operated freely, the country has become more dangerous for both journalists and aid workers to operate.
Earlier this week, consultancy group Humanitarian Outomes reported a record number of attacks on aid workers worldwide, with Afghanistan being the worst place for humanitarian staff to operate.
A string of attacks on journalists in the run up to the April 5 vote reflected this trend, with a Swedish-British journalist, an AFP news agency reporter and a veteran AP news agency photographer being killed in separate incidents.