A man has driven a van filled with gas bottles into the Australian Christian Lobby (ACL) headquarters in Canberra.
Australian Capital Territory Police said the incident was not "politically, religiously or ideologically" motivated.
The 35-year-old driver suffered serious burns after the explosion destroyed the vehicle and damaged the empty office.
The incident took place at 21:30 (10:30 GMT) on Wednesday and the man walked to Canberra Hospital for treatment.
Police said the man appeared to have ignited the gas cylinders within the vehicle.
But they ruled out political motivation after briefly speaking with him in hospital. He remains in a critical condition.
"We do not believe there is any threat to the community as a result of this particular incident," Commander Mark Walters said.
'Death threat' claims
Earlier on Thursday, ACL managing director Lyle Shelton said he believed it was a "targeted attack".
"We have received a number of death threats and threats of violence over the course of this year," he told the ABC.
"This is an attack on free speech in Australia which I am deeply shocked about and never thought I would see in my lifetime."
Mr Shelton said he was relieved no staff were present at the time.
What is the Australian Christian Lobby?
The ACL describes itself as a "grassroots movement" of more than 80,000 people seeking to bring Christian influence to public policy.
The conservative lobby is well known in Australia for opposing same-sex marriage, abortion, euthanasia and an LGBT education programme in schools. It supports Christian school chaplaincy and internet censorship.
Since the 2007 federal election, leaders from Australia's two main political parties have addressed conferences sponsored by the ACL.
The group is active on social media and often in the news, but some have questioned its influence beyond conservative politicians.
The ACL has also been criticised by some religious leaders who say it does not represent the views of all Christians.