(CNN) Malaysian Prime Minister Mahathir Mohamad submitted his resignation to the country's king on Monday, his office announced, a shock move that could plunge the country into political crisis.

The surprise announcement comes amid speculation that 94-year-old Mahathir was attempting to form a new ruling coalition that would exclude his promised successor Anwar Ibrahim.

It is not clear who will be the next Prime Minister or whether general elections will be held.

Mahathir's party, the Malaysian United Indigenous Party (Bersatu) announced Monday it would be dropping out of the ruling coalition Pakatan Harapan in support of the prime minister.

"All members of the House of Representatives of the party are also out of Pakatan Harapan. All of them have signed the Oath to continue to support and trust Tun Dr Mahathir Mohamad as the Prime Minister of Malaysia," according to a statement from Bersatu President Muhyiddin Yassin.

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