The House of Representatives and the Senate of Thailand convened a joint seating on Thursday to deliberate three draft charter amendments, as rival protesters rallied near the parliament under police watch.

The three bills, proposed separately by the cabinet, the ruling Pheu Thai Party and the coalition Chart Thai Pattana Party, seek to amend the Section 291 of the constitution by establishing a Constitution Drafting Assembly (CDA). But the proposed details regarding structure and membership of the organ vary.

Under the cabinet bill, the CDA will include 99 members, out of which 77 will be elected by citizens in 77 provinces. The remaining positions will be filled by academics and law experts selected by the parliament.

The deliberation will take two days, with the Senate, the opposition and the coalition each given eight hours to speak for and defend themselves.

Were any of those bills approved, it will make way for an overhaul of the embattled 2007 Constitution.

The constitution, the country's 18th since the overthrow of absolute monarchy in 1932, was promulgated in August 2007 following the military coup that toppled ex-PM Thaksin Shinawatra. Some of the charters have since been under attack by pro-Thaksin politicians and academics.

The move to amend the constitution drew both support and criticism. Proponents, mostly pro-Thaksin red shirts, and opponents gathered in confrontation early Thursday outside the parliament, where around 150 police were deployed to maintain security.

The rally was peaceful and most of the protesters left the venue around noon.Tul Sitthisomwong, core leader of the dissenting multi-color shirts group, or The Network of Citizen Volunteers to Protect the Land, said they prepared to rally again on Saturday at Victory Monument, an intersection in downtown Bangkok frequented by political protestings.

The group had submitted an opposing letter signed by about 30, 000 people to Deputy House Speaker Charoen Chankomol, he added.

Some analysts worry PM Yingluck Shinawatra pushes for a new constitution to pave way for her brother's return. Abhisit Vejjajiva, the opposition Democrat Party leader and ex-PM, dismissed the government's attempt to rewrite constitution as " suspicious", saying it would drive more wedges in the country.