Mr Sharif's party says his ban is 'politically motivated'
The Pakistani government says that it will challenge a court decision barring the former Prime Minister, Nawaz Sharif, from standing for parliament.
Current Prime Minister Yousuf Raza Gilani said an appeal against the ban would be filed in the Supreme Court.
On Monday, the Lahore high court ruled Mr Sharif, who heads a faction of the Pakistan Muslim League, was ineligible to run in a by-election due this week.
It said that the ban was because of previous criminal convictions.
Those date back to the 1999 coup in which he was toppled from power.
Correspondents say Monday's ruling was a major political setback for Mr Sharif.
The government says it also plans to seek a postponement of the by-elections scheduled for Thursday.
The judges were appointed by Mr Sharif's rival, President Pervez Musharraf.
Mr Sharif (l) and Mr Zardari have been at loggerheads over the judges issue
Mr Sharif's Pakistan Muslim League-Nawaz (PML-N) has dismissed the ruling as "politically motivated".
Hundreds of PML-N supporters burned effigies and chanted slogans against the ruling on Tuesday in Islamabad and elsewhere.
In Mr Sharif's home city of Lahore, about 600 protesters blocked the road and burned tyres in the centre of the city.
Similar protests also took place in the central city of Multan.
Correspondents say that the court's decision has exacerbated tensions between the PML-N and the main party in the governing coalition, the Pakistan People's Party (PPP).
A PML-N spokesman, Sadiqul Farooq, said on Monday that the party would not appeal against the Lahore high court ruling because it "lacked confidence" in the judiciary.
"We're not going to make an appeal before the Supreme Court because we don't recognise them as constitutional courts," he said.
Mr Sharif has been demanding the immediate reinstatement of judges removed from office by President Pervez Musharraf during a state of emergency last November.
Information Minister Sherry Rehman said that the government hoped the Supreme Court would make a ruling that "recognises the will of the people".
Such a ruling could also help heal the rift in the coalition, she said.
"We want to keep the alliance intact and we are in contact with our allies," she said.
Mr Sharif was deposed as prime minister by Gen Musharraf in a 1999 coup and later sent into exile, but has re-emerged as a major force in the country's politics.
The PML-N was the second largest party in general elections in February that saw President Musharraf's allies routed.
Neither Mr Sharif nor Pakistan's other top politician, PPP leader Asif Ali Zardari, ran.
The BBC's Barbara Plett says Mr Sharif's party joined the coalition government with the expectation that its leader was now clear to run for office.
Since then, though, the coalition has foundered, and the court's decision may further strain the fragile, anti-Musharraf alliance, our correspondent says.