The director of an Australian Christian group that campaigns against gay marriage has disputed police claims that an incident where a van exploded after being driven into its office was not "politically, religiously or ideologically motivated".

The Australian Christian Lobby said the police made this judgement after a "very short" talk with the driver of the van, that was filled with gas bottles. The driver is in hospital with serious burns.

Lyle Shelton, managing director, said he was praying for the driver, aged 35.

But he also said his staff had received many threats of violence and even death threats this year.

The lobby is a prominent conservative Christian group, speaking out for traditional marriage and against a state-funded LGBT education programme.

He was not convinced by the police statement that there was no religious motivation behind the explosion.

"I'm not convinced you can come to that conclusion so quickly. There are just too many coincidences. Why here? Why at the ACL office with multiple gas cylinders loaded up in your van? It just doesn't make sense to me.

"It's a coincidence of gigantic proportions for this to be plausible and concluded so unequivocally, so quickly, to me just seems strange."

Last month a motion to hold national vote on legalising same-sex marriage was defeated in the Australian senate.
Same-sex couples can register civil unions in most Australian states but they cannot marry.

Canberra Times reported that police said gas cylinders inside the van were ignited late on Wednesday night outside the league offices in Deakin, 2.5 kilometres from Parliament House. The driver then walked to Canberra Hospital. The van was destroyed and the two-storey building was badly damaged. 

Shelton also criticised politicians who had labelled the league "bigots" and a "hate group", and said such language could help create a "permission structure" to people with an agenda against them.