Prime Minister Anneli Jaatteenmaki quit after a presidential aide Martti Manninen said she had lied to parliament when she claimed she had not solicited the summaries of classified documents he sent her prior to the March general elections.
Just days before the election, Jaatteenmaki cited confidential foreign ministry documents to support her claim that her predecessor Paavo Lipponen was supporting the United States over Iraq, in clear defiance of Finland's official stand of neutrality.
Jaatteenmaki went on to win the elections and oust her rival, but was subsequently accused of lying about how she got the papers, to which as head of the then-opposition Centre Party she was not supposed to have access.
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Jaatteenmaki told parliament she had "neither asked for nor got secret Foreign Ministry documents" but an aide to President Tarja Halonen said she had made such a request.
The aide Martti Manninen said that Jaatteenmaki, while in opposition as the Centre Party leader, had approached him before parliamentary elections asking him for information on Iraq.
"In the meeting Jaatteenmaki was interested in Iraq material and gave me a secret fax number for keeping in contact," he said.
Her resignation caps two tumultuous days after Manninen's admission that he leaked the information. Jaatteenmaki gave her resignation to President Tarja Halonen, who accepted it. She took office on April 17, making her Centre Party-led government the shortest non-caretaker administration in almost 60 years.
A spokesman for the Centre Party said it hoped to continue the government coalition, which groups it along with the Social Democratic Party (SDP) and the Swedish People's Party.
The resignation is a major setback for the Centre, which had only just returned to power after eight years.
A Centre Party official said no decision had been taken on who would replace Jaatteenmaki, but there was speculation that the position may be filled by Defence Minister Matti Vanhanen.