Leading article: President Zardari's gamble

Many thousands took advantage of a brief lull in the fighting to flee the Swat district of Pakistan, where government troops are engaged in a major offensive against forces of the Taliban. Escape was possible for only a few hours before the army reimposed the curfew. But if the exodus from the Swat Valley continues at its current rate, the region could be contemplating the biggest displacement of people since the partition of British India in 1947.

This vast movement of people, and the toll of human misery it represents, is the most immediate cost of the Pakistan government's latest effort to stall the Taliban's advance. Three months ago, Islamabad concluded a truce with rulers in the Swat district that included the recognition of sharia law there in the hope that peace, however uneasy, would curb the Taliban's appeal. The result, in the short term at least, was almost the reverse. The Taliban exploited the local peace to advance; at one point they were reported to be only 70 miles from Islamabad.

This seems to be when even the weak government of President Asif Ali Zardari decided that enough was enough. A relatively small offensive to dislodge the Taliban from the Buner region was followed by the much larger and longer-term operation now in progress. The Pakistani army claims it has killed almost 200 Taliban fighters in the past two days alone.

Much, however, remains uncertain, not least how far this offensive might have been co-ordinated with, or orchestrated by, the US. Both Mr Zardari and the Afghan President, Hamid Karzai, met President Obama last week to learn about the administration's plans to co-ordinate policy towards the two countries. Washington is also well aware that US air strikes, such as the one that killed more than 100 people in Afghanistan last week, risk simultaneously stoking hostility towards the US and undermining the governments in both countries.

To this extent, Pakistan's army offensive looks the wiser course, especially if it retains broad domestic support. The cost, though, should not be underestimated. High numbers of casualties and refugees, embittered Taliban and weak central government are a recipe for more instability.