AUSTIN (Reuters) - Authorities said on Thursday they believe the arson fire that destroyed the governor's mansion here two years ago was set by suspects tied to an anarchist group linked to a planned attack on the 2008 Republican National Convention in Minneapolis.

The Texas Department of Public Safety said that in reviewing surveillance video taken before the fire, investigators had identified a white Jeep Cherokee whose occupants were seen taking photos of the mansion four days before the blaze.

The DPS said it had been able to find the Jeep and that its owner -- who they did not name -- had admitted to driving the vehicle while the photos were being taken.

DPS said the Jeep's owner had subsequently identified two people who were riding with him that night and that one of them "has been placed in the downtown area the morning of the mansion fire."

All three are now considered "persons of interest" in the investigation, DPS said. All three have denied involvement in the arson, which did extensive damage to the 152-year-old structure but did not injure the state's Republican governor, Rick Perry.

Investigators said they had established "a direct link" from the persons of interest to an Austin-based anarchist group that was linked to a planned attack on the Republican National Convention in Minneapolis in September 2008, which involved Molotov cocktails.

Texas is offering a $50,000 cash reward for information in the case that leads to the arrest and conviction of those responsible for the fire. DPS released a sketch on Thursday of another man it considers to be a person of interest in the case.