WHEN the Soviet Union invaded Afghanistan in 1979, it triggered one of the largest refugee outflows since the second world war. For every year after until 2014, Afghanistan was the world’s biggest source of refugees. Most of those who fled crossed the border into Pakistan. By the end of last year 1.5m Afghans were living in Pakistan. Only Turkey hosts more refugees.

Now Pakistan’s government wants to send the Afghans back. On December 31st refugees’ “Proof of Registration” cards will cease to be valid, meaning that any of the 1.5m-odd previously documented refugees who remain in the country will be left in legal limbo. As for the 1m or so undocumented Afghans in Pakistan, the government says that from November 15th they will need visas to stay—something hardly any of them have. Although such deadlines have been extended or ignored in the past, there are signs that this time the government means business. It has forced banks to close refugees’ accounts, and mobile companies to disable their SIM cards.

Many Afghans are getting the message that they are no longer wanted in Pakistan. In August 60,204 Afghan refugees left, more than the number that departed during the whole of 2015 and a nearly 50-fold increase from June. The United Nations High Commissioner for Refugees (UNHCR) and the International Organisation for Migration (IOM) predict that 220,000 registered and 400,000 undocumented refugees will return to Afghanistan by the end of the year. In Islamabad, Pakistan’s capital, the Afghan ambassador to Pakistan recently told a gathering of refugees that “you belong in Afghanistan”.

But the Afghan government has problems of its own. It is already struggling to deal with 1.2m people who have had to quit their homes, mostly to escape fighting with the Taliban. The UNHCR only helps refugees who are registered, and the IOM will focus its efforts on the 20% of undocumented Afghans that are most vulnerable. The bulk of those who return will have to fend for themselves. Small wonder that, as the bitter winter looms, aid agencies fear another humanitarian crisis.

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Correction (September 19th): An earlier version of this article said that the Soviet Union's invasion of Afghanistan triggered the largest refugee outflow since the second world war. Both the partition of India in 1947 and the secession of Bangladesh in 1971 produced more refugees. Sorry.