Yemeni President Ali Abdullah Saleh says any transition has to be done in a constitutional manner, and power cannot just be handed to protesters.
In an exclusive interview with the BBC, Mr Saleh described weeks of protests against his 32-year rule as a "coup".
His comments came after he agreed to a plan that would see him step down, in return for immunity from prosecution.
Opposition parties welcomed the plan, but protesters are still pressing for Mr Saleh's immediate departure.
There were fresh anti-government demonstrations in the capital, Sanaa, and in other parts of the country on Sunday.
"No negotiation, no dialogue - resign or flee," protesters in the capital chanted.
At least 130 people have died during two months of protests in Yemen inspired by uprisings elsewhere in the Arab world.
Mr Saleh told the BBC continuing protests could escalate the crisis.
"You call on me from the US and Europe to hand over power," he said.
"Who shall I hand it over to? Those who are trying to make a coup? No. We will do it through ballot boxes and referendums. We'll invite international observers to monitor.
"Any coup is rejected because we are committed to the constitutional legitimacy and don't accept chaos."
He also claimed that Islamist extremists had infiltrated protest camps.
"Al-Qaeda are moving inside the camps and this is very dangerous," he said. "Why is the West not looking at this destructive work and its dangerous implications for the future?"
The transition plan was drawn up by Gulf Arab states belonging to the Gulf Co-operation Council (GCC).
Under it, Mr Saleh would hand over to his vice-president one month after an agreement is signed with the opposition, and presidential elections would follow a month later.
Mr Saleh, his family and his aides would gain immunity from prosecution.
The ruling General People's Congress party accepted the transition plan late on Saturday.
Parliamentary opposition parties welcomed it but said they would not join a transitional government before Mr Saleh left office, as provided for by the plan.
Mr Saleh's opponents have also rejected the idea of immunity for the president and his relatives.
They have also expressed scepticism that Mr Saleh would stick to the agreement.
One prominent activist, Abdulmalik al-Yusufi, said there was a consensus among demonstrators "on rejecting the initiative".
"The Gulf initiative addresses the problem as if it was a political crisis between two parties," he said.
"We have taken to the streets in a revolution that is demanding a comprehensive change."
Abdulhafez Muajeb, the leader of a protest movement in the Red Sea port of Hudaida, told Reuters: "We will escalate our protests until we force the president to step down immediately."
Yemen is the Arab world's most impoverished nation and, even before the current protests, it was becoming increasingly chaotic, with both al-Qaeda and separatist challenges to the government's authority.
Mr Saleh suffered a major political reversal last month when a slew of ministers and ambassadors resigned in protest at the shooting of 45 people at a demonstration in Sanaa.
The president promised earlier not to renew his presidency in 2013 or hand over to his son. He has made - and broken - similar promises in the past.
The US welcomed the announcement of the GCC transition plan. A statement from the White House urged all parties to "swiftly" implement a peaceful transfer of power.