PM Abdullah ridiculed Mr Anwar's pledge to take power
Malaysian Prime Minister Abdullah Ahmad Badawi has rejected the opposition's claim it has enough support to seize power, saying he is "here to stay".
Opposition leader Anwar Ibrahim said he had more than enough pledges of support from defecting government lawmakers to form a new administration.
He said he wanted to meet Mr Abdullah to discuss a handover of power.
But Mr Abdullah, facing criticism over a spate of detentions without trial, insisted he remained in charge.
"Why should I be pressured? It is mere dreams. If at all it is true, he would have announced it by now. The whole world would have known," Mr Abdullah said when asked if Mr Anwar's efforts would compel him to quit.
"Do you think he would ask for a meeting with me to discuss a transition? He would storm into my room with hundreds behind him, shouting victory. This is Anwar's style," he told a news conference on Tuesday.
Mr Anwar has been promising to oust the government for months, following large opposition gains at a general election in March.
On Tuesday, he said he had more than enough pledges of support.
Mr Anwar has yet to name any of the MPs who are "defecting" to him
"It is increasing by the hour. I am not joking," Mr Anwar said, according to AP news agency - but he failed to name any of his new supporters.
Mr Anwar needs 30 MPs to cross the floor to join its 82-strong bloc and seize a majority in the 222-member assembly.
Mr Anwar's opposition coalition has huge momentum behind it, but in spite of the pledge it was unlikely that he would be in power by the end of Tuesday, says the BBC's Robin Brant in Kuala Lumpur.
Our correspondent says Mr Anwar has increased pressure on the government - but adds that the same party has controlled Malaysia since it was founded 51 years ago.
However, there is no doubt the government is struggling, he says - and there is a growing sense that this could be the final act.
Mr Abdullah says that he remains undeterred.
"The government is strong, we are here to stay," he said.
His deputy Najib Razak, widely tipped to replace Mr Abdullah, repeated the assurances.
"I am confident that the Barisan government will continue to rule," Mr Najib said of the Barisan Nasional or National Front coalition, in which the United National Malays Organisation (UMNO) is the leading component.
"This is the politics of deception, deployed to deceive, and clearly it has not become a reality," Mr Najib said of Mr Anwar's campaign.
The government lost its two-thirds parliamentary majority in March for the first time since independence over half a century ago.
Mr Anwar appeared to be a spent force 10 years ago when he was jailed for corruption and sodomy. He is facing renewed allegations of sodomy which he insists are part of a political smear campaign.
He has yet to name any members of the government who have promised to defect to him.
He says that any government led by him would focus on rooting out corruption, and bringing new fairness to all of Malaysia's races, not only the politically dominant Malays.
On Monday, one member of the government resigned, in protest at the government's use of draconian security legislation to jail one opposition member of parliament, one blogger and a journalist on the weekend. The journalist has since been released.
Zaid Ibrahim did not link his resignation to Mr Anwar's campaign, and reports say Mr Abdullah has refused to accept it.
UMNO is expected to hold a meeting of its ruling council on Wednesday.