Saleh said the opposition, which is calling for his immediate departure, is trying to stage a coup, the BBC reported.
The president has offered to leave by the end of the year.
"Those who want to climb up to power through coups should know that this is out of the question. The homeland will not be stable. There will be a civil war, a bloody war," he said.
Saleh has also lost the support of many tribal leaders, The Wall Street Journal reported.
U.S. diplomats are trying to negotiate a solution to the impasse with Maj. Gen. Ali Mohsen al-Amar, who announced Monday he no longer supported Saleh, the Journal said. The general, Saleh's half-brother, commands tanks stationed around key government buildings in Sanaa while Saleh's son has set up tanks around the presidential palace.
The United States and Saleh have been allies against terrorist networks in Yemen, and the Saudi government supports him, fearing an unstable country on its southern border.
The wave of defections was set in motion Friday when 52 protesters were killed.
Abdel-Malik Mansour, Yemen's representative to the Arab League, told al-Arabiya he sided with the anti-government protesters. The former environment minister, Abdul Rahman al-Iryani, who was fired Sunday, also said he planned to join the "revolutionaries," the Arab-language broadcaster said.
Yemen's ambassadors to Pakistan, Qatar, Oman and Spain and the consul in Dubai all announced their support of the protesters.
Saleh asked Saudi Foreign Minister al-Faisal to mediate the crisis Monday and dispatched his foreign minister to Riyadh, al-Arabiya said.
France was the first Western power to call for Saleh's ouster, and French Foreign Minister Alain Juppe called Saleh's departure "unavoidable."