The Pakistani forces offensive in the Swat valley could be over in two or three days, according to a government official.

The forces have undertaken their most concerted offensive against an expanding Taliban insurgency that has raised fears for the nuclear-armed US ally's stability and the safety of its nuclear arsenal.

The focus of the fighting has been the former tourist destination of Swat, 80 miles northwest of Islamabad, which the Taliban virtually took.

But tension has also been rising in South Waziristan, an al Qaeda and Taliban stronghold, with military officials saying an offensive was likely there after Swat is secured.

The United States and the Afghan government have long been pressing Pakistan to root militants out of South Waziristan and other enclaves on the Afghan border, from where the Taliban direct their Afghan war.

Militants attacked a paramilitary force camp in Jandola, 50 miles east of Wana, the main town in South Waziristan, late on Saturday, security officials said.

An intelligence official in the region said: "Militants came in force and attacked a paramilitary camp and fighting lasted for eight hours. At least 40 militants were killed while four soldiers died."

A military spokesman said the militants had been pushed back after a heavy exchange of fire. Up to 15 militants and three soldiers were killed, he said.

There was no independent confirmation of the casualty estimates.

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