Bersatu president Muhyiddin Yassin has tightened his grip on the party by sacking secretary-general Marzuki Yahya.

According to a source, the senator received his termination notice yesterday. The letter was signed by Muhyiddin and dated March 18.

"Muhyiddin cited Article 13.9 of the party constitution to terminate him as secretary-general without any explanation," the source told Malaysiakini.

Malaysiakini has sighted a copy of the letter.

Marzuki, when contacted, confirmed he received the letter from Muhyiddin and that he was not told of the reason for his sacking.

The source said it was unsure if Marzuki's removal was valid as the constitution suggested that it had to be discussed by the supreme council and approved by the chairperson.

Bersatu's chairperson is Dr Mahathir Mohamad, who is at odds with Muhyiddin. Marzuki is a staunch Mahathir loyalist.

The secretary-general is a powerful position, tasked with implementing decisions made by the supreme council.

The secretary-general also plays a role in administering the divisional AGMs, which are scheduled to take place in April, culminating in a national AGM and election.

Asked if Mahathir was informed of Marzuki's termination, the source replied: "Of course not."

Mahathir is currently under quarantine at home after coming into contact with a person who tested positive for Covid-19.

"In the next one or two days, we have to see what is Tun's (Mahathir) response to this. Only then would we know (if the termination was valid)," said the source.

Mahathir and Muhyiddin's relationship soured after the latter played a pivotal role in the collapse of the Pakatan Harapan federal government.

Muhyiddin had led a group of Bersatu MPs out of the coalition and later formed a new coalition government with Umno, PAS, Gabungan Parti Sarawak and several other smaller parties.

These parties later agreed to support Muhyiddin as prime minister. He was sworn-in on March 1.

Mahathir commands the loyalty of a small number of Bersatu MPs and is opposed to Muhyiddin's premiership.