Pakistanis flee into Afghanistan
Pakistani refugees fleeing the military operation in the tribal area of Bajaur
The UN's refugee agency says 20,000 people have fled Pakistan's tribal area of Bajaur for Afghanistan amid fighting between troops and militants.
The UN High Commissioner for Refugees says almost 4,000 families have cd into Afghanistan's Kunar province.
Some 300,000 others have been displaced by fighting, although Pakistan says many have found shelter in the region.
The country's military has launched an offensive in Bajaur and says it has killed more than 2,000 militants.
However, the UN refugee agency, the UNHCR, believes that the majority of those who have left will return home after fighting stops in the Federally Administered Tribal Areas (Fata).
Cross border attacks
Announcing its estimates of the numbers of people who have cd the border into Afghanistan, the UNHCR In Afghanistan said more than 600 families had left Pakistan for Kunar in recent weeks.
A spokesman said the organisation would look out for the welfare of the displaced if they were unable to return home before winter sets in.
"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," Nadir Farhad told Reuters news agency.
"But if it continues, we will definitely provide them with... assistance... so we can get them through the winter months."
Recently the UNHCR asked donors for more than $17m (39.4m) in aid to help about 250,000 people displaced by fighting and floods in north-western Pakistan.
They said money was needed to provide relief items like tents, blankets and plastic sheets.
Pakistan's army is engaged in a fierce campaign against militants in the north-west of the country.
Attempts by the government in Islamabad to negotiate with militants in areas along the border with Afghanistan appear to have failed, correspondents say.
The country has been hit by a spate of recent suicide bombings widely blamed on militants - including a devastating attack this month on the Marriott hotel in Islamabad.
The bombing killed more than 50 people, most of them Pakistanis.
Militants use the tribal areas as a base for operations in Pakistan and across the border in Afghanistan.
The Taleban and al-Qaeda are believed to operate in these border areas after being pushed out of Afghanistan.
Their presence in the border regions have prompted a number of US attacks inside Pakistan.
Those attacks have angered Pakistan's government, and there have been incidents around the border involving Pakistani troops firing warning shots at US helicopters.