Dr Mahathir Mohamad's involvement with the opposition is to chart the political ascension of his son Mukhriz, claimed Rural and Regional Development Minister Ismail Sabri Yaakob.

He also alleged that the former premier is sore with Umno for sidelining his son.

"I think Mahathir had a plan for Mukhriz from the beginning. He is very disappointed with Umno for not giving his son a chance to rise in the party.

"That is his grudge against Umno, I believe his action of being together with DAP and others (in the opposition) symbolises this...," he told reporters in Bandar Baru Salak Tinggi today.