Thailand's junta chief on Friday ordered border checkpoints to be beefed-up after ex-prime minister Yingluck Shinawatra failed to turn up at a court date that could have seen her jailed, sparking rumours she has fled the country.

"I just learned that she did not show up (at court)," Prayut Chan-O-Cha told reporters.

"I have ordered border checkpoints to be stepped up," he said, including local and major routes out of the country.