Prime Minister Abhisit Vejjajiva's car was attacked by protesters Tuesday, escalating tensions a day before a massive anti-government rally that the leader said has sparked concerns of civil war in Thailand.

Abhisit was not hurt during the attack, but some of the vehicle's windows were smashed when about two dozen protesters converged on his motorcade as it left a hotel in Pattaya, about 90 miles south of Bangkok, said government spokesman Isara Suntornwat.

The protesters hit, kicked and banged the car with "hard objects" in a brief confrontation before the motorcade sped away, Isara said. Security officials then transferred Abhisit to another car before taking him back to the capital.

"I did not panic. I can still work normally," Abhisit told reporters in Bangkok.

The attack was the first violence targeting Abhisit, who took office in December, and the most aggressive action since anti-government protesters started a sit-in outside his Bangkok office two weeks ago to demand his resignation.

The protesters have called for tens of thousands of supporters nationwide to join a Wednesday rally. They plan to march from Government House to the home of King Bhumibol Adulyadej's top adviser, Prem Tinsulanonda, whom they accuse of masterminding the 2006 coup that ousted former leader Thaksin Shinawatra.

Abhisit went on national television Monday night to publicize the government's concerns about violence at the rally and to warn that security forces will do whatever is necessary to maintain law and order.

"We cannot allow a civil war or a people's revolution," Abhisit said Monday. "If the situation leads to a riot, the government cannot stand still."

The protesters are supporters of Thaksin, who has been addressing the rallies almost nightly via video link from exile. Thaksin was ousted for alleged corruption and convicted last year for abuse of power but retains widespread support among the rural poor majority that benefited from his populist policies.

Prem has denied the accusations but the rare public criticism of a king's privy councilor broke a taboo in Thailand where members of the monarchy and their aides are highly revered. Prem had been indirectly accused of orchestrating the coup before; the last rally outside his home in July 2007 turned into a riot in which more than 200 people were injured.

"We have a job to protect key institutions, protect good people and the respected elders of the country," Abhisit said.

More than 4,000 police will be deployed outside Prem's house and the prime minister's office Wednesday, said Bangkok Police Chief Lt. Gen. Worapong Chiewpreecha.

Any violence at the demonstration could undermine Abhisit's government as it prepares to host leaders from 16 Asian nations from April 10-12. Leaders from across Southeast Asia, China, Japan, South Korea, India, Australia and New Zealand are gathering in Pattaya, where Abhisit held his weekly Cabinet meeting Tuesday as part of summit preparations.

The protests are the latest episode in Thailand's long-running political turmoil, which has become a tug-of-war between Thaksin's supporters and opponents. Each is known by the color of shirts they wear at rallies, red for pro-Thaksin and yellow for anti-Thaksin.

Yellow-clad protesters dominated last year's protests and were the first to camp at Government House where they stayed for three months. They are credited with bringing down two governments run by Thaksin's allies, and their protest culminated in a weeklong siege of Bangkok's two airports in December, crippling the vital tourism industry at the start of the holiday season.

So far, the red-shirted demonstrators have not entered the Government House grounds, but Abhisit has avoided his office since the rally started on March 26.

The demonstrators say Abhisit, who was appointed by Parliament, came to power through illegitimate means and should step down to make way for an elected administration.