ISLAMABAD (Reuters) - Pakistan resumed the repatriation of Afghan refugees on Monday, sending nearly 1,200 people back across the heavily guarded northern Torkham border, an official at the United Nation’s refugee body said.

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Pakistan is home to the world’s second largest refugee population, with a total of 2.5 million Afghans living there. Many have been in Pakistan since the Soviet invasion in 1979.

Relations between the two countries have deteriorated significantly in recent years. Kabul and Islamabad blame each other for terrorist attacks on either side of the border.

After a series of attacks in Pakistan left more than 130 people dead in February, Islamabad shut down its border crossings with Afghanistan and began planning to build a fence along the 2,500 km (1,500 mile) border.

Human Rights Watch has accused the U.N. of allowing Pakistan to forcibly evict Afghan refugees in violation of international law. Rights activists say they expect little change this year in either Pakistani policies or the inability of the Afghan government and aid groups to support the tide.

Pakistan denies systematic harassment of the refugees by its authorities. It claims the country has demonstrated great generosity in hosting the Afghans despite its own economic limitations. The Afghans going home now are leaving voluntarily, it says.

However, the Afghans complain about constant harassment and a lack of citizenship rights for those who have spent decades living and working in Pakistan.

“My family moved to Pakistan in the early ‘80s,” said Abdul Wahab, who lived in Islamabad for more than 30 years. “My father sold carpets and operated a successful shop. He made sure he always paid his taxes. But we could not have a bank account or own property.”

Despite growing up in Pakistan, Wahab said, the weight of being a second-class citizen was too much to bear. In early 2016, before Pakistan began sending back Afghan refugees, Wahab packed up his carpets and moved the business back to Kabul.

The United Nations High Commissioner for Refugees (UNHCR) confirmed that voluntary returns resumed after a suspension due to winter weather.

Asked whether Pakistan’s hard-handed approach toward Afghans living within its borders for nearly 40 years had spurred the exodus, UNHCR representative Samad Khan said the reasons were varied.

“Some move for economic purposes or to unite with their families and others are moving due to border restrictions which have impacted their families,” he said.

According to Khan, 370,000 refugees volunteered to return in 2016 after Pakistan announced new repatriation plans. Human Rights Watch estimates another 200,000 undocumented refugees were shipped back to Afghanistan, where conflict and economic crisis have left the government struggling to maintain basic living standards

“We have sent back 194 families today and they are all voluntary returnees who registered for return,” Khan said.

A UNHCR spokeswoman in Geneva said officials do not know how many refugees may return to Afghanistan this year, but that so far around 24,000 Afghans in Pakistan have “expressed an interest” in returning in April and May.