Army chief Narongphan Jittkaewtae has ruled out any chance of a military coup to end the ongoing crisis, saying political problems must be solved by political means.
Asked on Monday about the chances of the coup requested by a group of royalists on Sunday, the army chief replied: "Below zero."
Royalists had called for a coup after thousands of anti-government protesters again rallied in support of demands for reform of the monarchy.
They later calmed down, instead opting to submit a petition giving the army their moral support in defending the royal institution.
Sunday's demonstration saw a brief scuffle after a water cannon was deployed against the protesters, who had broken through a police cordon near the Grand Palace.
Police later apologised but confirmed it was pure water, not laced with chemicals as protesters claimed last month.
Gen Narongphan said authorities had not taken action against all protesters, only those who broke the law, but admitted that there were people who wanted to instigate violence.
He also defended the way the police behaved during the rally, saying some protesters had lit firework-like objects that they were about to throw into the palace.
Military personnel were injured while providing security in the area, he said, adding that the army chief then gave a stern warning to the protesters not to enter the palace grounds.
Deputy Commissioner of the Metropolitan Police Bureau, Pol Maj Gen Piya Tawichai, said police had warned the protesters to stop trying to break through the cordon to enter prohibited areas surrounding the Grand Palace.
Police had to use the water cannon against them to prevent violence and damage to the government and royal property. Plain, non-chemical water was sprayed vertically, not horizontally, at the protesters, said Pol Maj Gen Piya.
Regarding smoke bombs found at Sanam Luang, he said such devices had been used in many locations where the protesters gathered on Sunday.
Police would examine these to determine whether they violated the Ammunition, Explosives, Fireworks and Imitation Firearms Act.
A police officer was also hurt by glass and bottles thrown by the protesters -- his head was cut and he needed stitches, Pol Maj Gen Piya said.
As for the protesters' mock red postboxes containing letters they had written for His Majesty the King, he said they were now being kept at Chana Songkhram police station. Asked if the letter writers would be prosecuted he said officers would first examine the contents to see if they was illegal.
Meanwhile, Piyarat Chongthep, aka Toto, the head of the "We Volunteer" group of security guards that provided security for the protesting People's Movement, said on Facebook that coloured smoke bombs were used to counter the police use of high-pressure water cannons against protesters.
Prime Minister Prayut Chan-o-cha insisted he had never dictated how the country's conflict must be solved.
"I listen to all sides. I still believe that talk is always the best solution to every problem," he said.
Protest leader Arnon Nampa said the military would not stage a coup since they thought the protesters would use this to revoke the charter.
"The solution is to compromise, like HM the King said. But how and when? I still see the two sides' efforts to prevent loss. I want them to remain strong and get through this together," he said.