Islamabad - Businesses remained closed and thousands held protest rallies in Pakistan's largest province of Punjab on Friday against President Asif Ali Zardari, the widower of slain former prime minister Benazir Bhutto.

Thousands of people thronged in Lahore, the provincial capital of Punjab, to register protest against a court ruling that banned the top opposition leader and two-time Premier Nawaz Sharif from elected office.

Sharif says Zardari's loyal judges gave the ruling on his orders, because of a criminal conviction after his government was ousted in 1999 by the then military chief Pervez Musharraf.

The court also nullified the 2008 election of his brother Shahbaz Sharif and removed him from the chief ministership of Punjab, a stronghold of the two brothers where more than 60 percent Pakistani population lives.

Local traders supported the Sharif brothers by keeping businesses closed across the Punjab, while activists from their Pakistan Muslim League-Nawaz (PML-N) party held demonstrations against the new civilian government, which came to power in last year's general elections after almost nine years of military rule.

Nawaz Sharif joined Zardari briefly after February 18 elections last year which saw a defeat of Musharraf's political supporters, and formed a coalition government. But he parted from the alliance after Zardari showed reluctance to reinstate the former chief justice Iftikhar Chaudhry, who had been deposed by Musharraf.

An independent-minded judge, Chaudhry, who is regarded with respect by large portion of the public because of his refusal to take dictates from military dictator Musharraf, has turned into a symbol of justice, supremacy of law, protector of human rights, and eventually a guaranteer of democracy in Pakistan.

The Sharif brothers have in recent months improved their political credentials by supporting Chaudhry and opposing those that were appointed to replace him and his colleagues by Musharraf. "The entire country is against these judges, the entire civil society opposes them," Sharif told a huge rally in Lahore on Friday.

But Sharif's conflict with Zardari has thrown the militancy-plagued nuclear power into political turmoil, and raised concerns among Western nations who want to see the two to unite against the bigger threat, Taliban and al-Qaeda militants.

"It's now vital that whatever the political differences between President Zardari, Nawaz Sharif, the leader of the opposition --- come together to unite against the mortal threat Pakistan faces," British Foreign Secretary David Miliband told BBC on Friday.

"This is a very grave situation and it's intimately linked to the situation in Afghanistan. It's getting worse in a number of respects."

"The tempo of terrorist attacks has risen and the combination of political uncertainty, economic decline ... and then the security side mean that this is a particularly challenging time for any government.

"The degree of political disunity that exists at the moment is only contributing to the problem," he added. (dpa)