Samoa has been plunged into a constitutional crisis as the woman who won an election last month was locked out of parliament and the previous leader claimed he remained in charge.

It was the latest twist in a bitter power struggle that has been playing out in the Pacific nation since it elected its first female leader.

Prime minister-elect Fiame Naomi Mata’afa and her supporters showed up at parliament on Monday to form a new government, but were not allowed inside.

She and her FAST Party later took oaths and appointed ministers in a ceremony held under a tent in front of the locked parliament, actions that opponents said were illegal.

The nation’s Supreme Court had earlier ordered the parliament to convene, and the constitution requires that politicians meet within 45 days of an election, with Monday being the deadline.

But Tuilaepa Sailele Malielegaoi, who was prime minister for 22 years before his unexpected election loss, does not appear ready to give up power.

Ms Fiame’s election win was seen as a milestone not only for Samoa, which is conservative and Christian, but also for the South Pacific which has had few female leaders.

Last month’s election initially ended in a 25-25 tie between Ms Fiame’s FAST Party and Mr Tuilaepa’s HRP Party, with one independent candidate.

The independent candidate chose to go with Ms Fiame, but meanwhile, the electoral commissioner appointed another HRP candidate, saying it was required to conform to gender quotas making it 26-26.

The head of state – Tuimalealiifano Va’aletoa Sualauvi II – then stepped in to announce fresh elections to break the tie and they were scheduled to be held last week.

But Ms Fiame’s party appealed against the plans and the Supreme Court ruled against both the appointed candidate and the proposal for the new elections, restoring the FAST Party to a 26-25 majority.