A van filled with gas bottles has exploded after it rammed into the headquarters of the Australian Christian Lobby (ACL) in what police have ruled out as a targeted attack.

ACL managing director Lyle Shelton tweeted the incident last night, saying a vehicle had rammed its office in Canberra just after 9:30pm.

Mr Shelton added that staff were safe, and photos he shared showed a burnt-out van in the car park near the building’s entrance.

About 10:30am today ACT police confirmed a 35-year-old Canberra man had crashed into the building, igniting gas cylinders in the van and causing an explosion.

The man was the only person injured in the incident and was taken to hospital with serious burns, where he remains in a critical condition.

In a statement, police said their brief questioning of the man revealed his actions “were not politically, religiously or ideologically motivated”.

The man was not previously known to police.

A closer view of the car bomb driven into the ACL office in Canberra tonight. Shocked that this could happen in Australia. pic.twitter.com/GxJQZLTFQr

— Lyle Shelton (@LyleShelton) December 21, 2016

Initially Mr Shelton was describing the blaze as a “targeted attack” on “free speech in Australia”.

We have received a number of death threats and threats of violence over the course of this year that we have reported to police.

“This is an attack on free speech in Australia, which I am deeply shocked about and never thought I would see in my lifetime.”

Federal Justice Minister Michael Keenan said there were “no ongoing safety issues for the ACT community”.

Windows blown out in explosion

Mr Shelton said the ground floor windows of the ACL’s offices were blown out by the force of the explosion.

“Fortunately none of our staff or the tenants in the building were there,” he said.

“The building was vacant, it was after hours, so none of our people were injured.”

The van has been removed from the site but part of its tyres have melted onto the concrete.

Two days ago, a vehicle burst into flames after being rammed into a building only a few kilometres away in Fyshwick.