[Above: Supporters of ousted Thai prime minister Thaksin Shinawatra force their way as a glass door shatters at one of the venues of the 14th ASEAN Summit and Related Summits in Pattaya April 11, 2009.]

BANGKOK (AFP) - Tanks and armoured vehicles rumbled across Bangkok on Sunday as Thai premier Abhisit Vejjajiva cracked down on protesters leading the most serious challenge yet to his four-month rule.

One day after wrecking a summit of Asian leaders, demonstrators fired into the air and attacked his convoy as he was being driven away from the interior ministry where he had imposed a state of emergency minutes earlier.

In a day of fast-moving developments, his deputy Suthep Thaugsuban appealed to soldiers and police to enforce the state of emergency amid signs they were reluctant to intervene.

"Police and military -- you must carry out your duty to your best ability and restore normalcy as soon as possible," said Suthep, who is responsible for implementing the measures.

"I... will take all responsibility for all your actions," he added. "These are not constitutional demonstrators. They have injured senior officials."

The latest escalation in the country's chronic political turmoil came after police arrested the leader of activists loyal to ousted former prime minister Thaksin Shinawatra who had targeted Saturday's summit.

"I want to tell protesters that you have no right to break the law, or to restrict other people's rights," Abhisit said. "Otherwise the government must implement further measures under the state of emergency."

As tanks and soldiers fanned out, television showed red-shirted protesters armed with sticks and paving slabs smashing a car they mistakenly believed was carrying the prime minister and a separate vehicle carrying Suthep.

An army spokesman said troops had been deployed across the capital. An AFP reporter saw a tank and troops standing by on a road in central Bangkok close to government buildings.

Colonel Sunsern Kaewkumnerd told AFP a combined force of army, navy and air force had been deployed to ensure the security of public buildings, junctions and transport hubs at 50 spots in Bangkok and its surroundings.

"They are armed and we have also deployed armoured cars because protesters have used taxis to block the road," he added.

Pro-Thaksin protesters took to the streets two weeks ago demanding Abhisit quit. They say he came to power illegitimately through a parliamentary vote in December after a court forced Thaksin's allies from government.

The chaos in Bangkok is a virtual replay of crises last year that ended up forcing out two premiers loyal to Thaksin, who was toppled in a military coup in 2006 and remains in exile.

The army has generally shied away from confronting protesters since action against riots in 1992 left dozens dead, and police moves against anti-Thaksin demonstrators last October left two dead.

It is the third time in eight months that authorities have declared a state of emergency in Bangkok.

The move allows police to disperse protesters by banning public gatherings of more than five people and empowering police and military to detain suspects for up to 30 days without charge.

Abhisit is under intense pressure to curb the unrest after the humiliating cancellation of Saturday's regional Asian summit, after which authorities were forced to evacuate foreign leaders, some of them by helicopter from the hotel roof.

The weekend summit was supposed to discuss the global financial crisis and North Korea's rocket launch and included the leaders of China, Japan and South Korea plus 10 Southeast Asian nations.

Protesters earlier regrouped in their thousands outside Abhisit's offices, as well as the interior ministry and a courtroom where judges were to rule on the detention of protest leader Arisman Pongreungrong.

Police said they arrested the former pop singer at his Bangkok home "on the charge of inciting protesters to kidnap the prime minister and cause unrest in the country."

Thaksin remains in exile to avoid a two-year jail term for corruption, but has rallied supporters -- and incensed the government -- with almost nightly video and telephone speeches from an unidentified foreign hideout.