REUTERS, KABUL- Some 20,000 people from Pakistan's northwestern tribal region of Bajaur have fled to Afghanistan this summer due to intense fighting between government forces and militants, the United Nations said on Monday.
The Pakistani military launched an offensive in August for control over the strategically key region of Bajaur and have been involved in heavy fighting since then.
"More than 3,900 families, or around 20,000 individuals, have fled fighting in Bajaur ... into Kunar province in eastern Afghanistan," said the United Nations High Commission for Refugees (UNHCR) in Afghanistan.
"In the last two weeks alone, over 600 Pakistani families have fled into Afghanistan," it said.
Bajaur is the smallest of Pakistan's seven so-called tribal agencies, semi-autonomous ethnic Pashtun regions along the Afghan border, with a population of one million people.
U.S. officials say Taliban and al Qaeda-linked fighters, financed by drug money, use the tribal regions as an operating base to launch attacks inside Afghanistan, where Western forces are struggling to stem a growing insurgency.
Around 9,000 Pakistani soldiers are deployed in Bajaur and up to 1,000 militants have been killed in clashes this month, according to the Pakistani army.
Several hundred thousand people have fled their homes because of fighting, seeking refuge in other parts of the country or in neighbouring Afghanistan.
"They have mainly been provided accommodation by relatives and friends," UNHCR spokesman Nadir Farhad told reporters. But some 200 families are already living without shelter, he said.
UNHCR has been coordinating aid efforts and hopes the refugees will be able to return soon but said it was prepared for the winter.
"It's very difficult to predict the security situation on the other side of the border but what we hope is that the security gets better and people will be able to go back," he said.
"But if it continues, we will definitely provide them with ... assistance ... so we can get them through the winter months."
Around 70 percent of the families are Pakistani, said Farhad, the remainder being Afghan.
In the past, refugees crossed the other way, to escape from violence in Afghanistan. Some four million Afghans escaped civil war in the 1980's and 1990's seeking refuge in Pakistan. More than half have now returned.
While Pakistani refugees have crossed into Afghanistan to escape tribal or sectarian violence in previous years, this recent influx is biggest yet.