Q+A: Thailand's intractable political crisis

BANGKOK (Reuters) - Anti-government protesters besieged Bangkok's main airports on Thursday, forcing flight cancellations and stranding travelers in the latest twist in a six-month street campaign to unseat the government.

The People's Alliance for Democracy (PAD) movement has vowed to stay until Prime Minister Somchai Wongsawat quits, which he has refused to do.

The following Q+A examines some of the main issues:

WHY DID POLICE ALLOW PAD TO STORM AIRPORTS, WILL THEY BE EVICTED?

Police are desperate to avoid a repeat of October 7, when two people were killed and hundreds injured in clashes outside parliament, and so simply melted away when the protesters approached the $4 billion Suvarnabhumi airport on Tuesday.

The PAD are armed and were happy to shoot at police lines last month, suggesting any attempt to remove them by force could result in scores of casualties, increasing the chances of military intervention.

Other possible reasons for police inaction range from incompetence to orders being quashed by bigger forces such as the army or palace.

HOW DOES AIRPORT SIEGE HELP PAD'S CAUSE?

The chaos is costing the PAD public support, especially as tourism, which employs 1.8 million people, will suffer badly.

But its ultimate goal is to make Bangkok ungovernable and trigger a putsch against a government they say is a pawn of ousted and exiled leader Thaksin Shinawatra.

Under an interim military government, the PAD would then have more chance of advancing its "new politics" agenda to ensure a parliament stuffed with appointed grandees.

Some of the PAD's plans are codenamed "Hiroshima" and "Nagasaki," and their ideologues have been quoted on the need for political assassinations.

WHO IS BACKING PAD?

The alliance of royalist businessmen, academics and activists says it gets 1 million baht ($28,000) a day from the public.

Analysts suspect it is also bankrolled by anti-Thaksin business interests, parts of the army and palace figures, including Queen Sirikit, who attended the funeral of a PAD supporter killed in clashes with police.

WHAT'S THAILAND'S KING GOT TO DO WITH CRISIS?