Kevin Rudd, the Australian foreign minister, has resigned, his office said Wednesday, amid speculation that he may mount a leadership challenge to Prime Minister Julia Gillard.

The Australian news media has been abuzz in recent days with reports that Rudd was considering contesting Gillard's leadership of the governing Labor Party.

Gillard unseated Rudd as prime minister in June 2010 after he lost support within the party.

Ranya Alkadamani, a spokeswoman for the Foreign Ministry, confirmed that Rudd had resigned while in Washington.