Federal Opposition Leader Tony Abbott has expressed regret for appearing to endorse the abusive behaviour of some protesters at an anti-carbon tax rally in Canberra.
"I think a few people went over the top," he told reporters in Canberra.
"Naturally, I regret that. But I can understand why people feel very passionate."
Earlier, a lycra-clad Mr Abbott was reluctant to answer reporters' questions as he prepared to cycle from Parliament House to nearby Narrabundah for the launch of the annual Pollie Pedal charity ride.
Mr Abbott on Wednesday spoke to the Canberra rally in front of placards with slogans like "Ditch the witch", while one banner labelled Prime Minister Julia Gillard "Bob Brown's bitch.
Both the government and the Australian Greens have called on Mr Abbott to apologise to Ms Gillard for appearing to endorse the derogatory sentiments of some protesters outside Parliament House.
Mr Abbott urged "everyone inside and outside the parliament" to conduct the carbon tax debate with respect.
"If the prime minister had been straight with the Australian people before the election, we wouldn't be in quite the situation we are now in," he said.
Climate Change Minister Greg Combet earlier demanded Mr Abbott disassociate himself from the protesters' behaviour in a more formal manner, saying some of the slogans and placards were extremely offensive.
"I really think he needs to do that in a decisive way. He needs to apologise for being associated with it," he told ABC Radio on Thursday.
Mr Abbott would not indicate whether he would apologise to Ms Gillard when the pair meet later on Thursday to discuss the federal intervention in Northern Territory indigenous communities.
Opposition MPs defended their leader on Thursday, with one frontbencher accusing the government of double standards.
"The ALP website right now is comparing Tony Abbott with a Nazi war criminal," climate change spokesman Greg Hunt told ABC Radio.
Another Liberal frontbencher, Sophie Mirabella, said the rally was an expression of people power.
"The reason so many were angry was that they felt they had been lied to," she said, referring to Ms Gillard before the election saying she would not introduce a carbon tax.
Most of the protesters were "ordinary and normal" people who had been demonised by the government to keep them quiet.
"They are not going to be shut up by the glib spin of the prime minister and Mr Combet."
Ms Mirabella defended the use of the word "liar" to describe Ms Gillard, but baulked at defending the use of "bitch" to describe the prime minister.
Senator Brown, who has written to the prime minister expressing his disgust at the behaviour of some protesters, says the posters were "particularly offensive, really quite disgusting".
"The amazing thing for me is that politicians of such experience as Tony Abbott and his senior colleagues ... did nothing about the banners," he told ABC Radio.
"They took them as part of the ambience."
Mr Abbott, having had time to reflect on it, owed Ms Gillard an apology, Senator Brown said.
