ISLAMABAD (Reuters) -- Street fighting has erupted in the main town of Pakistan's Swat valley as security forces mount a new phase of their offensive against Taliban militants, the military said.
The military began their operation in the Swat valley and neighboring districts earlier this month to stop the spread of a Taliban insurgency.
"Street fighting has begun in Mingora," military spokesman Major General Athar Abbas told a news conference on May 23.
He said government forces had cleared some parts of the city but fierce clashes were under way in the center of Mingora, and 17 militants had been killed so far in the day.
Nearly 1.7 million people have been displaced by the Swat offensive, while about 555,000 people had been forced from their homes by earlier fighting in the region.
The United Nations has warned of a long-term humanitarian crisis for Pakistan and on May 22 launched a $543 million "flash appeal" for the displaced.
One day earlier, donors promised $224 million, including $110 million from the United States. The government has said the militants could exploit a failure to help.
The United States, which sees Pakistan as vital to its plan to defeat Al-Qaeda and bring stability in Afghanistan, has applauded Pakistani resolve to fight what some U.S. leaders have called an "existential threat" to the country.
However, Pakistan could face greater turmoil in the months ahead.
Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, has said a U.S. military offensive in southern Afghanistan could push Taliban fighters into Pakistan.
The United States is pouring thousands of extra troops into Afghanistan this year to try to reverse gains by a resurgent Taliban, particularly in its southern heartland, bordering Pakistan.
Pakistani political parties as well as the public largely support the Swat offensive but analysts have said the backing could evaporate if many civilians are killed or if the displaced families are not given enough help.
Abbas said the operation in Mingora was likely to be slow as security forces wanted to avoid civilian casualties.
He said the majority of the residents of Mingora had already moved out and only 5-10 percent of the population was still in the town. He feared that militants could use them as "human shields" or make them hostages.
"The pace of the operation will be painfully slow. So be patient but the operation has started and inshallah [God willing] we are going to take it to a logical conclusion," Abbas said.
Pakistan says more than 1,000 militants and more than 50 soldiers have been killed in the fighting. There has been no independent confirmation of those estimates.
About 15,000 members of the security forces are taking part in the offensive.
Abbas said around 1,500 to 2,000 "hardcore" militants were believed to be involved in fighting in Swat as a large number of criminals who had ganged up with the Taliban had fled the region.