An Uzbek asylum-seeker accused of ramming a truck into a crowd of people in Stockholm last week, killing four people, had tried to travel to Syria in 2015 to join the Islamic State group, an Uzbekistan security source said on Wednesday.

The source, who spoke on condition of anonymity, said the suspect, Rakhmat Akilov, was an ethnic Tajik who came under the influence of a Tajik Islamic State cell while living in Sweden. Akilov has been living in Sweden since at least 2014.

Akilov was detained at the Turkish-Syrian border in 2015 and deported back to Sweden, the source said. The source added that in February this year Uzbekistan's authorities had put him on a wanted list for people suspected of religious extremism.

Swedish security police declined to comment on the information, citing the ongoing investigation.

Police believe Akilov, 39, whose asylum application failed and was wanted for deportation at the time of Friday's attack, hijacked a beer truck and drove it into a busy pedestrian street in the Swedish capital before crashing into a department store.

Akilov has confessed to committing a terrorist crime, his lawyer said on Tuesday. A judge has remanded him in custody for a month while investigations continue.

Swedish security services have said Akilov had figured in intelligence reports but they had not viewed him as a militant threat.

Sweden's state migration agency declined to comment on the Uzbekistan security source's remarks.