BANGKOK - A JOINT parliament session of elected MPs and senators was postponed on Monday after thousands of anti-government demonstrators surrounded the building, house speaker Chai Chidchob said.

Parliament had been due to convene at 9.30 am (10.30am Singapore time), but early on Monday thousands of supporters of the People's Alliance for Democracy (PAD) protest movement blocked all the entrances to the building, witnesses said.

'The meeting today (Monday) is impossible. I will call the next meeting when the situation improves,' Mr Chai told parliament radio.

Mr Chai gave no indication of when parliament would meet next, and said it was difficult to move the joint session of the upper and lower houses to a new location because of procedural rules and regulations.

PAD leaders have called on supporters to join them in a 'final battle' on Monday in their six-month campaign to topple the government, which they accuse of being a corrupt puppet of ousted and exiled Thai premier Thaksin Shinawatra.

Police said about 18,000 protesters descended on the streets outside parliament, and PAD leader Pibhop Dhongchai proclaimed the postponement of the session a victory for their movement.

'It was a success that we managed to stop the meeting because the meeting would have discussed the constitution, which would help the government,' he told reporters.

The PAD says government plans to amend the charter are aimed at helping Thaksin escape corruption charges, but parliament officials had insisted that amendments to the constitution were not on Monday's agenda.

Lawmakers had instead planned on deliberating 25 international agreements that the government may have to sign at the summit of regional bloc Asean in the northern Thai city of Chiang Mai next month. -- AFP