Thousands of Afghan families have been fleeing Pakistan to escape harassment after a deadly Taliban attack on a school in Peshawar last December, the head of the International Organisation for Migration (IOM) in Afghanistan said.
More than 30,000 undocumented migrants flocked across the border at Torkham in January, Matthew Graydon, IOM's Information and Reporting Officer told Al Jazeera on Sunday.
A figure substantially higher than reported in 2014.
Taliban fighters attacked a local school in Peshawar on December 16, killing more than 130 children and prompting Pakistan to step up operations against Taliban hideouts located along the border with Afghanistan.
Co-operation between Pakistani and Afghan forces has improved since the attack, leading to the arrests of numerous suspects in Afghanistan, where officials believe the attack was planned.
When something horrible happens, people start taking it out on foreigners
Since the attack, many Afghans living in Pakistan are reporting more incidents of harassment such as raids on their homes and police coercion, the IOM has said.
"It all started with the attack on the school in Peshawar," Richard Danziger, head of IOM's mission in Afghanistan told the Reuters news agency.
"When something horrible happens, people start taking it out on foreigners."
Many Afghan families leaving the country have been in the country for decades and have nowhere to go once they reach Afghanistan, Danziger said.
"Their lives are in Pakistan," he said.
The flow of undocumented migrants has risen from 350 in the first week of January, to 1,400 in the final week of the month.
Danziger said it was difficult to predict when the number of migrants would slow down.
The sudden arrival of thousands of people has put increased pressure on Afghanistan's already limited resources with only the most vulnerable receiving assistance.
"We are down to helping the most desperate there," Danziger said, adding that resources had been diverted from the Iranian border.
Those families who qualify for help receive medical care, food and shelter, but the IOM says it needs approximately $1.6m to cope with the additional 17,000 people who have returned this year.
Many refugees have headed to nearby provinces such as Kunar where fighting between Afghan forces and Taliban fighters has intensified.
Many families have fled to Jalalabad city, a major trading hub, Graydon told Al Jazeera.
Some have headed to nearby provinces such as Kunar where fighting between Afghan forces and Taliban fighters has intensified.
Others have trekked to Kabul, where resources for thousands of internally displaced people settled in the capital are already heavily strained.
Source: Al Jazeera and agencies