Posted Sun May 24, 2009 12:19am AEST Updated Sun May 24, 2009 5:08am AEST
Pakistani security forces have entered Mingora, the Swat Valley's main city, and killed at least 17 Taliban militants as a new phase of their offensive against the militants began, the military said.
The military offensive in the Swat Valley and neighbouring districts earlier this month to stop the spread of a Taliban insurgency that had raised fears for nuclear-armed Pakistan's future.
"Street fighting has begun in Mingora," military spokesman Major-General Athar Abbas told a news conference.
He said government forces had cleared some parts of the city but fierce clashes were underway in the centre of Mingora.
The United Nations has warned of a long-term humanitarian crisis and called for massive aid for nearly 1.7 million people displaced by the Swat offensive and about 555,000 people who had been forced from their homes by earlier fighting in the region.
On Friday (local time) the United Nations launched a $US543 million "flash appeal" for the displaced.
This came after donors on Thursday promised $US224 million, including $US110 million from the United States.
About 15,000 members of the security forces are fighting between 4,000 and 5,000 militants in Swat, the military says.
Officials have warned that the militants might try to strike back, although the government has vowed to expand the offensive once it is completed in Swat.
Before Saturday's fighting, Pakistan had said more than 1,000 militants and more than 50 soldiers had been killed in the offensive.
There has been no independent confirmation of that estimate of casualties.