The turmoil is the latest episode in an eight-year conflict that pits Bangkok's middle class and royalist establishment against the mostly poorer, rural supporters of Yingluck and her brother, former premier Thaksin Shinawatra.
At a celebration to mark national Children's Day on Saturday Thailand's army chief, Prayuth Chan-ocha, said he feared an escalation in violence next week.
(Read more: In Thailand, rallying cry is against too much democracy)
"I am concerned about security because there will be many people. The violence is increasing...," said Prayuth. "We can think differently but we cannot kill each other. Please don't use violence."
Many Thais believe the military will soon step in to break the political deadlock, especially if the protests turn violent, and rumors of an impending coup have intensified.
The army has staged or attempted 18 coups in 81 years, but it has tried to remain neutral this time.
The authorities say they will deploy more than 14,000 troops and police on Monday, including police at the main airport, to maintain order in the streets.