The Stockholm District Court ruled there was enough evidence against Andrei Zamyatnin to keep him detained.
He was initially ordered to remain in custody until March 3, but that deadline was extended by two weeks, before being extended one more time today.
Zamyatnin was working as a visiting researcher at the Swedish University of Agricultural Sciences in Uppsala when he was arrested last month.
Security police have refused to disclose what country he is accused of working for, or elaborate on the nature of the espionage allegations.
The arrest of Zamyatnin has angered Russia, which has demanded his swift release.
(AFP, Reuters)
