UPDATE 4-Thai protesters hit police, tighten grip on airport

(Recasts with latest checkpoint incident, tourism warning)

By Ed Cropley

BANGKOK, Nov 29 (Reuters) - Anti-government protesters tightened their grip on Bangkok's international airport on Saturday, attacking police checkpoints aimed at stopping more people from joining the blockade.

The protests, aimed at forcing out Prime Minister Somchai Wongsawat, have paralysed flights, stranded thousands of passengers and sparked rumours of a military coup, even though the army chief has said he will not seize control.

The government said tourism was suffering and the number of visitors to Thailand could fall by half next year.

In the latest clash, about 150 riot police fled their checkpoint near Suvarnabhumi airport after they were assaulted by protesters hurling iron rods and firecrackers from speeding cars.

The People's Alliance for Democracy (PAD) movement, which invaded the airport four days ago, then stationed guards on the expressway exit to prevent the police returning.

Earlier, about 2,000 PAD members forced riot police to abandon another checkpoint near the airport. There was no violence, but one police officer was detained by PAD "security guards", the Nation newspaper reported on its website.

The PAD's occupation of Suvarnabhumi, and a second older airport in Bangkok, is a dramatic escalation of their six-month street campaign against Somchai.

The airport closures have crippled the tourism industry during the peak end-of-year season. Somchai, who has refused to quit, imposed emergency rule at the airports two days ago but police have made no moves to evict the thousands of protesters.

Somchai, who is running the government from its political stronghold in the northern city of Chiang Mai, demoted his national police chief on Friday. While no official reason was given, Thai newspapers said he had been sacked for refusing to send riot police in to end the protest.

"SHOOT THEM BACK"

The PAD, a coalition of royalist businessmen, activists and academics who accuse Somchai of being a puppet of his brother-in-law, ousted prime minister Thaksin Shinawatra, seized the airports in a "final battle" to unseat the government.

At Suvarnabhumi, PAD youths armed with iron stakes and wearing police riot helmets manned barricades, scanning with binoculars for signs of police or pro-government gangs.

"If they come, we'll not open the door. If they shoot us, we'll shoot them back. We'll die if that makes the country better," PAD leader Sondhi Limthongul told supporters, the most explicit admission yet by the movement that they are armed.

His co-leader, retired general Chamlong Srimuang, said the PAD had not held talks with authorities, but was open to meet "with people directly involved in the situation such as Somchai".

In a televised address on Friday night, Somchai said the PAD was doing massive damage to the tourism- and export-driven economy, but he would avoid violence to end the protests.

"Don't worry. Officials will use gentle measures to deal with them," he said, inviting rights groups and journalists to monitor the imposition of emergency rule at the two airports.

The airport sit-ins have forced hundreds of flights to be cancelled and grounded millions of dollars of air cargo.

Deputy Prime Minister Olarn Chaipravat said the damage to Thailand's tourist image may cut arrivals by half in 2009 from an expected 13.5 million this year, and threaten one million jobs.

The government will spend $30 million over the next month to help stranded tourists, he told reporters, including giving them free hotel rooms and a daily stipend of $56.

"It has been very frustrating," said Ian Fraser, an Australian who was due to return home on Wednesday after a month of lectures in Thailand.

The government is shuttling tourists to U-Tapao, a Vietnam War-era naval airbase 150 km (90 miles) east of Bangkok, as an alternative landing site for airlines, but travellers have complained of massive delays and confusion.

Pressure is building on the army to oust the prime minister, as they did Thaksin in 2006, after Somchai rejected military calls to quit this week.

But army chief Anupong Paochinda has said he would not take over, arguing the military cannot heal fundamental political rifts between the Bangkok elite and middle classes, who despise Thaksin, and the poor rural and urban majority who love him. (Additional reporting by David Fox and Orathai Sriring) (Writing by Darren Schuettler; Editing by Mark Trevelyan)