Rival formations on Saturday stepped up their campaign for the presidential election with Prime Minister Manmohan Singh [Images] meeting Samajwadi Party leader Amar Singh to mobilise support for United Progressive Alliance-Left nominee Pratibha Patil.

On the rival front, National Democratic Alliance convener George Fernandes [Images] met SP chief Mulayam Singh Yadav and is believed to have lobbied support for Vice President Bhairon Singh Shekhawat, who may be fielded as an independent candidate backed by the NDA.

UPA-Left nominee Pratibha Patil, who arrived in the capital on Saturday, met UPA chairperson Sonia Gandhi and the prime minister, and announced that she would resign as Rajasthan Governor before she files her nomination.

After a half-hour meeting with the prime minister, Amar Singh said there was no discussion between them on the presidential election but disclosed that the prime minister had talked to Yadav seeking SP support for Patil.

However, the All India Anna Dravida Munnetra Kazhagam, hosting a meeting of the leaders of the Third Front in Chennai on Sunday, said the Front would 'choose a nominee' for the presidential election.