Umno members who are adamant on criticising the party should be brave enough to quit, said Minister in the Prime Minister's Department Azalina Othman Said.

"If you continuously open your mouth, behaving in a manner that gives strength to the opposition [...] then you should be gentlemen enough (to quit). Be a man and leave.

"It is a free country, those who are unhappy should just go," she told reporters at the sidelines of the Umno general assembly in Kuala Lumpur today.

Another option, she said, is for them to wait and contest in the next party polls.

Umno has postponed its internal elections until 2018, amid mounting pressure for its president Prime Minister Najib Abdul Razak to resign.

Asked if she was referring to former premier Dr Mahathir Mohamad and Umno deputy president Muhyiddin Yassin, Azalina replied: "It can be anyone."

She said Mahathir was free to speak his mind, but warned there would be repercussions.

"If Mahathir believes strongly in his conclusions and theories, this is a free country, he can continue to speak.

"But whoever wants to say anything be careful of defamation and slander," she cautioned.

Mahathir has repeatedly called for Najib to resign, claiming that Umno might lose the next general election if he remains at the helm.

He has also accused the prime minister of numerous misdeeds, including attempting to bribe him.

Najib, on the other hand, has denied any wrongdoing and described the accusations as being part of a conspiracy to topple him.