A year after an election returned Pakistan to civilian rule, the country has slid back into a political crisis.
Authorities banned protests and police began rounding up activists on Wednesday, the eve of the launch of a protest movement by anti-government lawyers and opposition parties.
The trouble comes as new concern has arisen about the ability of the US-ally to stem a rising tide of Islamist militancy after last week's attack on the Sri Lankan cricket team.
Meanwhile, the economy is being propped up by the International Monetary Fund but needs more external support.
What is the protest about?
The cross-country protest motor convoy, known as a long march and due to begin in the south on Thursday, fuses two strands of opposition to the government led by the party of President Asif Ali Zardari, husband of the late Benazir Bhutto.
Anti-government lawyers campaigning for an independent judiciary have been joined by the political opposition.
The protest is aimed at securing the restoration of a former chief justice of the Supreme Court, Iftikhar Chaudhry, sacked by former president and army chief Pervez Musharraf in 2007.
Analysts say Zardari fears if Chaudhry is reinstated, he could nullify an amnesty that Musharraf granted Bhutto and Zardari to enable them to return to Pakistan without fear of prosecution for old charges of corruption.
The political parties can mobilise the support of thousands of party workers to reinforce the lawyers. Protest organisers plan a sit-in outside parliament in Islamabad from March 16.
The government says the rally should not enter central Islamabad. Protest organisers say their plans are still on, despite the ban on processions.
Why is the Opposition up in arms?
Former prime minister and opposition leader Nawaz Sharif, who heads the country's second-biggest party, is furious with Zardari after the Supreme Court last month effectively barred Sharif and his politician brother, Shahbaz, from contesting elections.
Shahbaz Sharif's victory in a by-election last year was nullified, and he was disqualified from holding the office as chief minister of Punjab, the most populous and most influential of Pakistan's four provinces.
Zardari then imposed central rule, known as governor's rule, in Punjab for two months, and threw out the provincial government of the Sharifs' Pakistan Muslim League (Nawaz) (PML-N).
The Sharifs have accused Zardari of being behind the court decision and their supporters have taken to the streets.
Both Sharif and Zardari covet Punjab -- politicians say whoever controls the province that returns more than half the members of the National Assembly controls the country -- but neither has a clear majority in the provincial assembly.
Bhutto's Pakistan People's Party (PPP) and the Sharifs' party were bitter rivals in the 1990s, a turbulent decade in which Bhutto and Sharif both served as prime minister twice without completing a term. A military coup in late 1999 ousted Sharif and brought Musharraf to power.
Analysts fear a return of the politics of confrontation between the country's two biggest parties.
What's at stake?
Pakistan's latest attempt at democracy is at risk.
Musharraf's successor as army chief, General Ashfaq Kayani, has vowed to keep the army out of politics. But, the danger is that if the crisis becomes acute, the military, which has ruled for more than half the country's 61 years of history, will feel forced to act.
The army has little reason to back Sharif, even if Zardari is widely unpopular and disliked by hawkish elements who distrust his pro-West stance and dovishness towards India.
Sharif had bad relations with at least three army chiefs during the 1990s. Morever, the West is wary of Sharif, believing that he panders to the religious/nationalist constituency that opposes the war on terrorism.
The United States wants Pakistan to focus on fighting the Taliban and al Qaeda, and doesn't want the army to be diverted by politics, or, analysts say, drawn into helping Sharif.
Beleaguered stocks and the rupee, which both fell sharply last year, have been under pressure on worry about politics.