What does the report say?
Pakistan has long been a host to millions of Afghans who fled to neighbouring states following political turmoil and the Soviet occupation of their country in 1978.
Roughly 2 million refugees still live in Pakistan, making it one of the top refugee-hosting countries in the world.
But in 2016, around 570,000 Afghan refugees were forced to return by Pakistani authorities, said a report by Human Rights Watch (HRW). The report also said the United Nations High Commissioner for Refugees (UNHCR) was "complicit in these violations."
Most of the people – roughly 365,000 – were registered refugees, meaning they had disclosed their status to the government and were guaranteed protection under international law.
"This coerced exodus amounts to the largest unlawful mass forced return of refugees and asylum seekers in the world in recent times," HRW said.
Why are they being forced to leave?
The repatriation drive is not new. The UNHCR has helped 3.8 million Afghans return home since 2002.
But what happened last year was unprecedented.
Both Pakistan and Afghanistan have been battling militancy and often blame each other for instigating attacks.
Relations took an ugly turn in December 2014 when terrorists attacked a school in Pakistan's northern city of Peshawar and killed 145 people, including 132 children.
Within a few weeks, Pakistan introduced a new strategy to combat militancy, giving broader powers to security agencies.
As part of that strategy, Afghans were also to be repatriated, even though investigators found no evidence of their involvement in the attack, said the HRW.
Officially, the Pakistani government says the move to send the refugees back to Afghanistan is due to security and economic reasons.
Did deteriorating relations play any part in this?
The strict scrutiny of the Afghan refugees came at a time when Afghanistan was cementing economic and diplomatic ties with India, Pakistan’s next-door arch rival.
A trade deal signed in May 2016 allows Iran and India to use Afghanistan as a transit route to export goods to Central Asia and Russia, bypassing Pakistan entirely.
Islamabad saw the trade pact as growing Indian influence in the region.
Then in June 2016, Pakistani and Afghani troops clashed on the Torkham border, leaving a Pakistan major and an Afghan soldier dead.
This strained relations further.
How are the refugees being forced out?
Every refugee needs a Proof of Registration (POR) card. These were issued by Pakistan’s government between October 2006 and February 2007 to 2.1 million Afghans. The POR serves also serves as an identification card. New cards have not been issued.
The card used to be valid for up to 3 years but since late 2015, the validity is being extended irregularly – sometimes for only three months. This has created uncertainty among the refugees.
In many instances the cards are not being renewed at all, said HRW, which based its findings on more than 100 refugee interviews.
Afghans who became part of the exodus said they sensed a sudden rush of hostility towards them in 2015.
The HRW report said Pakistani landlords also pushed the rents of their apartments and shops up. The police routinely stopped the refugees and if their POR was expired, they were taken away to police station and released only after they paid money.
The HRW report also said many schools for refugee children were forcibly shut.
Why is the report accusing UNHCR of being involved?
Every refugee returning to Afghanistan used to get $200 from the UNHCR. In June 2016, this amount was increased to $400, becoming a "critical" factor in persuading the cash-strapped refugees to leave, said HRW.
This amount comes to around $2800 per family, a significant sum considering many of the refugees live in the poorest slums in Pakistan.
In Karachi, Pakistan's largest city, many Afghan children roam the streets, collecting garbage and plastic bottles that they sell to recyclers to support their families.
Through the increased cash grant, HRW said, the UNHCR encouraged refugees to return to Afghanistan, where an ongoing Taliban insurgency continues to claim lives.
UNHCR was reprimanded for remaining silent when refugees were returning, primarily because of police abuse and fear of deportation.
Sudden deportation is particularly scary for the refugees since they stand to lose homes and businesses they have invested in for decades.
Pakistan has mostly looked the other way on the question of undocumented refugees. But deportations started to go up in 2014, when 10,000 were sent back. The number jumped to 20,000 in the following year, and then to 22,559 in 2016.
What is the Afghan government’s reaction?
Afghanistan has bolstered the return of refugees by promising land and other benefits to those who come back under a campaign called "One’s Own Homeland", says HRW.
The Afghan government promised to give refugees residential land, drinking water, schools and hospitals.
"In reality, no landless Afghan returning from Pakistan in 2016 received – or had the slightest prospect of receiving – any land in 2017."
Pakistan has rejected the HRW findings.