A court in southern Germany has sentenced an Eritrean asylum seeker to life for stabbing two teenage girls, one of them fatally.

The 27-year-old man, identified only as Okba B, attacked the girls in the town of Illerkirchberg in December.

The 14-year-old, called Ece, died from 23 stab wounds and her friend aged 13 was critically injured.

Prosecutors said he attacked them after they saw his knife, which he intended to use at a local immigration office.

They said he was angry over officials' failure to issue him with a passport, which he needed in order to get married in Ethiopia.

The verdict judged his crime to be "particularly severe", meaning he is very unlikely to get early release after serving 15 years in prison.

The Eritrean had arrived in Germany in 2015, during an unusually large influx of asylum seekers, many of them refugees fleeing war and persecution.

The court in Ulm found that before last November he had integrated normally into German society, with a job, knowledge of German and a calm personality.

Okba B told the court he regretted his act and asked the families for forgiveness.

The verdict can still be appealed. But if it stands, prosecutors say, he could be deported during his prison term.

The case triggered much outrage in Germany, but the girls' families said they did not want it to be exploited politically by anti-immigration groups. The girl who died was German from a Turkish-origin family.