Ahead of his swearing-in as the president of Pakistan, Asif Ali Zardari on Monday appealed to estranged ally Nawaz Sharif to rejoin the Pakistan People's Party-led government, but the Pakistan Muslim League-Nawaz chief refused to budge, even as he assured "healthy" cooperation in strengthening democracy.

Zardari asked Sharif to return to the alliance when the latter met him to congratulate him on his win in last week's presidential poll.

Senior PML-N leader Ahsan Iqbal, who was present at the meeting, said Sharif told Zardari that the party would play a "healthy role in the opposition".

The PML-N pulled out of the alliance last month after accusing Zardari of reneging on several promises, including restoration of judges deposed by former president Pervez Musharraf [Images].

Iqbal described the meeting between Sharif and Zardari as a "courtesy call" and said the two sides did not have any detailed political discussions.

Zardari is set to be sworn in as president on Tuesday and Sharif would be unable to attend the event as he will leave the same day for London [Images] to be with his wife, who is recovering after a surgery.

"He (Sharif) will be away for the next five-six days, so he wanted to personally congratulate Zardari before he left the country," Iqbal said.

On the eve of the oath-taking ceremony, 53-year-old Zardari moved into the presidential palace amid brief religious ceremonies.

Shortly after Musharraf resigned last month, Zardari had shifted from his private residence to the Prime Minister's House citing security concerns.