Bangkok - Nine bombs exploded across Bangkok as the Thai capital celebrated the New Year, killing two people and driving thousands of revelers home after the city was forced to cancel festivities.

Hospital staff and officials said 34 people were injured, at least six of them foreigners including one American.

There were two waves of bombings. Six nearly simultaneous explosions late Sunday night killed at least two people and injured 26. Some initially mistook the sound of the bombs for fireworks.

Bangkok Mayor Apirak Kosayothin canceled major public celebrations and sent home about 5,000 gathered in Central World Plaza, the downtown venue for Bangkok's main New Year countdown party.

After midnight, three more bombs went off near the same plaza, iTV television reported. Eight people were injured in the later blasts, the report said.

There was no immediate claim of responsibility for the bombings, which capped a year of unrest in Thailand that included a military coup three months ago and a mounting Muslim insurgency in its southernmost provinces.

National police chief Gen. Ajirawit Suphanaphesat said he did not believe insurgents were behind the attacks in Bangkok, a major international banking and technology hub for Asia.

Police and army troops wielding assault rifles guarded some entertainment venues, transit stations and busy traffic circles. Roadblocks were up on some streets, while hotels stepped up security, searching cars and canceling expensive New Year's Eve dinners.

Major public celebrations were also canceled in the northern city of Chiang Mai.

But festivities continued in some areas of Bangkok, including the city's most famous red light district, Patpong Road, where hundreds of foreign tourists carried on celebrating. At midnight, fireworks lit up the sky in both Bangkok and Chiang Mai, with many residents still gathered in the streets of both cities.

Several embassies' Web sites advised their citizens to avoid Bangkok's city center.

"There is a possibility of further attacks in coming days," said a travel advisory from the Australian Department of Foreign Affairs and Trade. "Australians are urged to avoid unnecessary travel in Bangkok."

Bomb attacks are rare in the Thai capital.

Following the first wave of bombings, police said two people died at hospitals. There were also 14 people seriously wounded, said Health Minister Mongkol Na Songkhla.

"I heard a loud explosion and I thought it was fireworks. I ran there and saw a bleeding woman at the bus stop," Somrak Manphothong, a receptionist at the Saxophone bar near site of the first bombings. "Another guy was lying on the floor, covered with blood, and his wife was shaking his body."

At another site near a vegetable market in the Klong Toey slum, a pool of blood and egg yolks covered the roadside beside an overturned motorcycle.

The three bombs that exploded just after midnight Monday were in a phone booth, a hotel, and near a canal bridge in a touristy downtown area packed with hotels and shopping malls.

The six foreigners were injured in the second set of blasts, according to officials at the Police Hospital. They said one was an American. Doctors were trying to save a Hungarian woman's badly injured leg, said hospital spokeswoman Warin Detkung, denying earlier news reports that both her legs had been blown off.

In September, Prime Minister Thaksin Shinawatra was ousted in a bloodless coup by Gen. Sondhi Boonyaratkalin. The military installed Surayud as the interim prime minister until elections in October 2007.

But Thaksin still enjoys widespread support and a number of arson attacks in provincial areas have been blamed on his followers.

"There are two potential suspects, Muslim insurgents and Thaksin's residual power," said Thitinan Pongsudhirak, a political scientist at Chulalongkorn University. "I tend to think it's residual power. I suspect the previous regime."

Thaksin's lawyer denied the former prime minister's involvement in the bombings on the Web site of the newspaper Matichon.

Bombings and shootings occur almost daily in Thailand's three southernmost provinces of Yala, Narathiwat and Pattani, where an Islamic insurgency that flared in January 2004 has killed more than 1,900 people.

Muslims make up the majority in overwhelmingly Buddhist Thailand's deep south, where they have long complained of discrimination.

The insurgents have carried out numerous attacks in the south, but are not known to have launched any in Bangkok.