BANGKOK: Thai police fired tear gas and water cannon at protesters on Tuesday (Nov 17) in a bid to push back a demonstration at parliament demanding constitutional changes that would touch on the powerful monarchy.
At least 18 people were hurt in the most violent confrontation since a youth-led protest movement emerged in July.
Protesters are demanding changes to the constitution drawn up by Thailand's former military government. They also want the removal of Prime Minister Prayut Chan-o-cha, a former army ruler, and reforms to curb the powers of the monarchy.
IN PHOTOS: Thai protesters, police clash outside parliament
READ: Thai lawmakers debate demands for constitutional changes
Police sprayed water cannon at protesters who tried to cut their way through razor-wire barricades. Then they fired tear gas at the hundreds of demonstrators.
Ambulances ferried the injured to hospital. Bangkok's Erawan Medical Centre said 18 people were hurt, 12 of them suffering as a result of teargas. It said one of those hurt was a police officer.
CNA correspondents saw protest frontliners screaming and running as police fired several shots of tear gas and water to disperse the crowd.
Some protesters shouted in pain after being hit by the blasts of water, which stung their skin on impact, with some observed to have thrown up after.
Live television images showed water cannon being fired against an advance guard of anti-government protesters who arrived with helmets and masks and tried to remove the coils of wire.
Protesters threw back coloured smoke bombs at police.
"Dictator's lackeys!" the Free Youth protest group posted on Twitter with pictures of the helmeted riot police using the water cannon.
Police declared that protests were banned within 50m of the area. Hundreds of protesters assembled nearby.
"Protesters tried to break through the barricades to enter the restricted area," police spokesman Kissana Phathanacharoen told reporters.
Government spokesman Anucha Burapachaisri said police had been obliged to act to keep parliamentarians safe.
Hundreds of royalists had earlier demonstrated to call on lawmakers not to change the constitution.
Lawmakers were discussing several proposals for the way in which the constitution can be amended - some of which would exclude the possibility of changes to the way King Maha Vajiralongkorn's monarchy is treated under the constitution.
READ: Thai king calls for unity after protesters turn back on motorcade
WATCH: Impact of Thai protests on its immediate neighbouring countries
There is also discussion of the role of the Senate, which was entirely selected by Prayut's former military government and helped ensure that he kept power with a parliamentary majority after a disputed election last year. Prayut says the vote was fair.
Opposition parliamentarians have also called for changes to the constitution.
Protests since July initially targeted Prayut and constitutional change, but have since called for the monarch's role to be more clearly accountable under the constitution and for the reversal of changes that gave the current king personal control of the royal fortune and some army units.
"Amending the constitution is going to lead to the abolition of the monarchy," royalist leader Warong Dechgitvigrom told reporters at the demonstration.
Protesters have said they do not intend to abolish the monarchy.