Pakistan remains on a knife edge despite President Musharraf's nationwide appeal for calm. The burial yesterday of Benazir Bhutto brought thousands of chanting supporters to the family mausoleum where she was interred beside her father. Many were berating their head of state, shouting “General killer, Army killer” and vowing revenge on the President and the Army, whom they accuse of complicity in her assassination. Across the country, mobs clashed with police and set fire to cars, shops, banks and any symbols of state authority. In Karachi the shops were shuttered and police patrolled the streets after more than 2,000 people attacked a police station and set it on fire. In Sindh, the home province of the Bhutto family, protesters threatened “revolution” against the Punjabdominated military Establishment.

Now, more than at any time since he seized power, President Musharraf's leadership is being tested. The killing of Ms Bhutto was as much an attempt to overthrow his authority as it was to wreck the return to democratic politics. All the evidence points to al-Qaeda extremists as the perpetrators: as in Iraq, their aim is to use suicide bombings and assassinations to make the country ungovernable and then impose their own authority. They knew that the likely victory of Ms Bhutto's Pakistan People's Party in the January elections would, as the West hoped, have consolidated the informal alliance with Mr Musharraf. That, in turn, would have increased the pressure on the Islamists and entrenched the pro-Western and anti-Taleban policies in Islamabad.

Nevertheless, it is not only PPP supporters who are voicing suspicions that disaffected elements in the Army or in Pakistan's nebulous intelligence service may have been involved in the plot. They, too, had much to lose from a Bhutto victory, fearing that their privileges and influence would have been affected. Amid inflammatory conspiracy theories, the suggestion that the security protection for Ms Bhutto was culpably slack or that sympathisers in the military may have helped the bomber's infiltration is believed widely, adding to the public anger directly at President Musharraf.

He now must show the leadership that his country so desperately needs. He must demonstrate the decisiveness and political impartiality that have been so lacking in recent months, to regain the respect and confidence not only of his own disillusioned countrymen but also of the outside world. For Mr Musharraf remains the only leader able to take tough decisions and the only politician who has shown any readiness to confront the extremists and separatists who threaten to pull Pakistan apart. He still has the backing of America and Britain, though his antics have strained their patience. It is time to repay that trust. That means, first of all, deciding what to do about the elections. Tempted though he may be to reimpose martial law or postpone the vote, he must base any decision on proper consultation. The PPP may still be eager to go ahead, hoping to cash in on Ms Bhutto's martyr image. But it may still need another month to select a new leader. If there is to be a postponement, a new date, in the near future, must be set.

Mr Musharraf must also move swiftly to avert civil war. That means the deployment of troops and police to halt rioting, proper and impartial protection of all political leaders and meetings, and a much more vigorous response to the threats by al-Qaeda and religious extremists. There has long been a suspicion that, in his manoeuvrings to remain in office, he has reached out too far to extremists. He has made deals to withdraw the Army from the tribal lands, gone soft on the pursuit of al-Qaeda and delayed the confrontation over the Red Mosque. All that must end: a commitment to restore democracy must equally mean a commitment to crush the enemies of democracy.

Mr Musharraf has long argued that, like his hero Kemal Atatürk, he must remain in power to save his country from extremism and disintegration. Pakistan stands on the brink of both. This is truly his Atatürk moment.