By Alison Bevege
SYDNEY (Reuters) - Australia's citizenship crisis has taken a new twist as another member of parliament resigned on Saturday, threatening the narrow majority of Prime Minister Malcolm Turnbull's ruling coalition.
The constitution bars dual nationals from parliament, and Turnbull's centre-right coalition government was thrown into disarray last month by a High Court ruling that five of them were ineligible to be lawmakers.
On Saturday, Conservative Liberal party MP John Alexander told reporters he was no longer certain that he was solely Australian, and that meant he had to resign.
"It is my obligation that I must resign," Alexander told a news conference in Sydney. "That's what I will do. I think there is a great need for certainty, to clarify the situation and to do so as expeditiously as possible."
Alexander had been waiting for Britain's Home Office to clarify whether he held British citizenship by descent. It is not known whether they responded.
He would have to confirm sole Australian citizenship before fighting a by-election to regain his seat.
Alexander said he planned to contest the by-election which The Sydney Morning Herald said must be announced no later than Monday, to allow the minimum 33-day campaign required to hold the poll on December 16.
Turnbull must rely on two independents to vote with his coalition to safeguard his position and block the passage of legislation his government opposes.
Only the two independents now guarantee his position after the High Court ruling expelled three members of the Liberal-National coalition government from parliament, with a fourth resigning days later, after confirming his dual nationality.
(Reporting by Alison Bevege; Editing by Clarence Fernandez)