Prime Minister Najib Abdul Razak has opted for the silent treatment when asked if he will have a one-on-one debate with Dr Mahathir Mohamad.

He merely smiled and left without answering, after attending the launch of Kojadi SME Loan Scheme and the Secretariat for the Advancement of Malaysian Entrepreneurs (Same) in Kuala Lumpur this afternoon.

Earlier today, Najib ( photo ) had not showed up at the event titled "Nothing To Hide: PM's Dialogue with NGOs" due to the event being cancelled by the police who cited security reasons.

However, former premier Mahathir who attended the event this morning, gave a speech in Najib's absence.

Mahathir was stopped mid-speech by the police and eventually agreed to leave the stage. He later gave a press conference.

Previously, Mahathir had said he was ready to have a public debate with Najib anytime.

Najib instead chose to reply to criticism from the former prime minister through blog posts and have never definitively answered Mahathir's challenge to a debate.

At the event this afternoon, MCA president Liow Tiong Lai told Najib to "be firm" and that he has their support and backing.

"We are all behind you," Liow said.