Islamabad - Pakistan's most influential Islamist political party on Monday announced it will join former premier Nawaz Sharif's protest march against a court ban on his candidacy and for the reinstatement of the deposed Supreme Court chief justice.

"We will fully participate in the long march," Jamaat-e-Islami chief Qazi Hussain Ahmed told reporters at a joint press conference with Sharif in Lahore, the capital of Pakistan's eastern province of Punjab.

The Supreme Court last week upheld an earlier high court verdict that banned Sharif and his brother, Shahbaz, from parliamentary post because of a previous conviction.

The court decision also removed Shahbaz from the seat of chief minister of Punjab, the richest and populous province in Pakistan.

Sharif has asked the nation to stand up to the pro-Western government of President Asif Ali Zardari, the widower of assassinated former prime minister Benazir Bhutto, accusing Zardari of influencing the court judgment to remove him from active politics.

"These are defining moments. The entire nation has to come out (on the streets)," Sharif said on Monday.

The alliance with the Islamist group is likely to boost the protests by Sharif's Pakistan Muslim League-Nawaz (PML-N) party that continues to stage countrywide agitations since last week, blocking main roads and closing markets, particularly in Punjab, the PML-N's stronghold.

The development has raised concern in Western capitals that internal political turmoil might divert Pakistan's attention away from fighting Taliban and al-Qaeda militants.

Zardari and Sharif earlier forged an alliance after trouncing the political supporters of former military strongman Pervez Musharraf in February 2008 elections.

But they parted ways after six months over Zardari's reluctance to reinstate deposed top judge Iftikhar Chaudhry, who was removed by Musharraf.

Sharif said Zardari was not reinstating Chaudhry as he feared that the independent-minded adjudicator would reverse a controversial National Reconciliation Ordinance
(NRO) by Musharraf, which cleared Zardari of graft charges. (dpa)