Former prime minister Tun Dr Mahathir Mohamad would never join the opposition or support their campaign in the Rompin and Permatang Pauh parliamentary seat by-elections, said Kedah Menteri Besar Datuk Seri Mukhriz Mahathir.

"This is all nonsense. Don't hope for him to want to weaken the party (UMNO and BN) and support Pakatan Rakyat. The issue of him supporting the opposition does not arise at all," he said.

Mukhriz said the situation came about following the putting up of a mischievous opposition poster suggesting that Dr Mahathir would be going to Rompin and Permatang Pauh to campaign for Pakatan Rakyat while this idea was ridiculous.

Mukhriz, who is also Kedah BN chairman, said Dr Mahathir's action of frequently voicing his opinions including criticising the government was being capitalised by the opposition parties to make it look as though the former premier was supporting the opposition.

Dr Mahathir's criticism against Prime Minister Datuk Seri Najib Tun Razak was also not aimed at weakening UMNO and Barisan Nasional (BN), he told reporters after attending the 'Kenduri Rakyat' programme in Tanah Liat Mukim 9, here, Monday.

Mukhriz said if studied carefully, the statements and views that came from his father were for the good of UMNO and BN.

He said it was that Dr Mahathir was prime minister for 22 years, so he had his own views but which were meant to strengthen the party.

"If we look at his statements, he hopes BN will win in (the by-elections in) Rompin and also Permatang Pauh. Whatever his opinion, it is for the sake of strengthening the party and never to weaken it," he said.

Mukhriz was asked on Dr Mahathir's criticism against the government and the prime minister, causing him to be regarded as the de facto opposition leader.