In a dramatic move, Australian Foreign Minister Kevin Rudd resigned on Wednesday saying he could no longer work without the support of Prime Minister Julia Gillard, amid speculation that he may pose a bitter challenge to her leadership.

“The simple truth is that I cannot continue to serve as Foreign Minister if I don’t have Prime Minister Gillard’s support,” 54-year-old Rudd said at a media conference in Washington DC, which was broadcast live in Australia.

“I therefore believe the only honourable course of action is for me to resign,” he said.

A “disappointed” Gillard, who ousted Rudd as Prime Minister in June 2010, said he did not inform her in advance that he would resign.

“I am disappointed that the concerns Mr Rudd has publicly expressed ... Were never personally raised with me, nor did he contact me to discuss his resignation prior to his decision,” 50-year-old Gillard, who was in Adelaide, said in a short statement.

Rudd’s sudden resignation came amid signs that he was preparing for a showdown by challenging Gillard for leadership in the ruling Labor party’s upcoming caucus this week. It also followed claims by supporters of the Prime Minister that she was prepared to sack the Foreign Minister for disloyalty.