A chartered Czech plane with the Afghans on board, all of them men, took off late yesterday from the eastern German city of Leipzig and arrived in Kabul today.
Eleven of the deportees had criminal records for acts including manslaughter, causing grievous bodily harm, the sexual abuse of children, fraud and theft, interior ministry spokeswoman Annegret Korff told reporters.
The other three Afghans had refused to cooperate on establishing their identity, she added.
Saxony state interior minister Markus Ulbig told public broadcaster MDR that Germany was sending a "loud and clear message" that those not granted refugee status following an official review "no longer have a right to be in Germany".
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Around 150 demonstrators gathered at the airport in Leipzig to protest against the expulsions.
In Berlin, leading Greens MP Claudia Roth called on the government to stop the deportations, noting that some 250 people were killed in attacks in Afghanistan in the last week.
"Under these conditions, expulsions to Afghanistan clearly violate our responsibility to provide humanitarian protection," she said in remarks reported by DPA news agency.
That group of eight Afghans represented the sixth wave of repatriations of Afghans from Germany since December under a disputed Afghan-European Union deal aimed at curbing the influx of migrants.
Amnesty International warned European governments earlier this month that a surge of failed Afghan asylum seekers "forcibly" returned are at risk of torture, kidnapping and death.
Almost 9,500 Afghans went back to their homeland in 2016 after their applications for asylum in Europe were rejected, compared with fewer than 3,300 a year earlier, the rights group said.
More than 13,300 Afghans have applied for asylum in Germany since the start of the year.
Chancellor Angela Merkel has been struggling to bring down the numbers of asylum seekers after the arrival of more than one million migrants - mainly from Iraq, Syria and Afghanistan - since 2015.