The Swedish PM's top aide, Ulrica Schenstroem, has resigned after media reports of an apparently drunken evening in a bar with a TV reporter.
It is unclear whether Ms Schenstroem was on duty that night
The reports had sparked intense debate over the appropriateness of the aide's behaviour, in view of her role of alerting ministers to emergencies.
Neither Ms Schenstroem nor Prime Minister Fredrik Reinfeldt have said whether she was on duty that evening.
Photos of her drinking with and kissing the reporter appeared in a local paper.
The previous Swedish government was accused of being slow to respond to the devastating 2004 Asian tsunami.
A top aide to former Prime Minister Goeran Persson resigned after an official investigation into the government's handling of the disaster, in which some 543 Swedes were killed.
'Under the influence'
There have been negative media reports about Ms Schenstroem since pictures of her drinking with the television reporter were published in the daily Aftonbladet last week.
The photos showed the pair apparently kissing, but the aide and the journalist, named as Anders Pihlblad, have both denied that they were romantically involved.
In a statement after her resignation, Ms Schenstroem apologised for her behaviour, saying she regretted being "engaged in conversation with a journalist and drinking wine in that context".
Mr Pihlblad told his own TV channel that Ms Schenstroem was "clearly under the influence of alcohol".
Mr Reinfeldt and other leaders of his centre-right coalition are refusing to comment on the resignation until after prime minister's questions.
The coalition has been hit by three ministerial resignations since it won the 2006 election, ending 12 years of rule by Mr Persson's Social Democrats.