German prosecutors are investigating whether a gunman who killed two American soldiers at Frankfurt Airport had links to Islamist groups.
A 21-year-old Kosovar man confessed to the killings on Thursday after being arrested and questioned a day earlier.
Officials said there was evidence linking him to terror cells in Germany.
Police spokesman Armin Thiel said that security at Frankfurt airport had now been stepped up.
“We now have an increased number of patrols, both plain clothes officers and armed units with bullet-proof vests and machine guns,” Thiel said.
US and German authorities are refusing to rule out that this was a terrorist attack.
The suspect posted comments on his Facebook account describing non-Muslims as “infidels,” as well as links to a jihadist fighting song.