The number of people displaced by fighting in Pakistan's northwestern Swat valley has risen to more than 1.4 million, U.N. humanitarian chief John Holmes said on Monday, according to AP.

"The situation is volatile and changing rapidly," Holmes told reporters at the United Nations.

He said extra financial resources were urgently needed to deal with the situation and that the United Nations would soon launch an emergency appeal for hundreds of millions of dollars to cover the costs of the refugees over the next 12 months.

Pakistan's government on Sunday urged people stranded by a military offensive against Taliban militants in Swat, an alpine beauty spot 80 miles (130 km) northwest of Islamabad, to try to get out.

Many civilians are believed to still be inside Mingora, the main town in Swat, after the army launched an offensive more than a week ago to stop the spread of Taliban influence.

Holmes said the number of people displaced by the most recent fighting is more than 1.4 million. That is a total of people registered with the Pakistan authorities, with the help of the U.N. High Commissioner for Refugees (UNHCR), he said.

The U.N. previously said it had registered 1.17 million people displaced by the fighting in the Swat area.

Holmes said that when including at least half a million more displaced by fighting since last August, the total is around 2 million to 2.1 million people.

"This is clearly a major humanitarian challenge for the government and all the aid agencies," said Holmes. "All the agencies are scaling up their efforts and their presence rapidly," he said.

Holmes said that 15-20 percent -- or around 250,000 -- of those registered are in some 24 camps, meaning that most people are with families, in rented accommodations or elsewhere.

UNHCR, which already had a major presence in Pakistan, has been distributing aid from the stocks it already had in the country and helping establish new camps as well as registration centers, Holmes said.

"There will need to be extra resources... and I expect a revised appeal to be published this week," said Holmes.