BANGKOK - Thailand's prime minister pledged on Tuesday to ensure that a major protest this weekend against his government would be peaceful but said he was concerned that outsiders might try to instigate unrest.

Prayuth Chan-ocha said he had instructed police to avoid clashes when demonstrators march on the seat of government on Saturday. He urged protesters to follow the law and prevent chaos.

Near-daily rallies since mid-July have demanded Prayuth's removal and changes to a constitution that opponents say helped keep him in power after an election last year, which the former junta leader insists was fair.

"The government will ensure the safety of people," Prayuth told reporters, urging the public to be "eyes and ears" and prevent trouble.

Protest leaders expect tens of thousands of people to march on Government House, piling more pressure on Prayuth's military-backed administration to dissolve parliament.

The demonstrations, though largely peaceful, have revived memories of more than a decade of intermittent unrest and protracted street rallies that culminated in a 2014 coup led by Prayuth against the government of Yingluck Shinawatra.

The upcoming march marks the anniversary of another coup in 2006 that ousted Yingluck's brother, Thaksin.

A dozen demonstrators have been arrested and later released over the rallies.

Protest leaders have said Saturday's rally would feature discussion about reform of the monarchy, until recently a taboo topic.

The interior ministry has sent a letter to university heads telling them to stop students demanding such reforms, which "could lead to violence".

It referred to 1976 and 1992 incidents when security forces killed scores of anti-government demonstrators. REUTERS