“Based on our intelligence, the rally will be intense with a huge turnout of protesters,” National Security Council chief Paradorn Pattanatabut told reporters.

The security law enables the government to prevent the use of certain routes or vehicles, impose a curfew, ban gatherings, carry out searches of buildings and censor the media.

Nearly 17,000 police will be deployed for the demo, according to officials. It will be the first major street protest against Yingluck’s 16-month-old government.

“Security agencies report that violence might erupt which would result in damage to lives and property,” said Varathep Rattanakorn, minister to the prime minister’s office.

Politically turbulent Thailand has been rocked by a series of sometimes violent rival street protests in recent years, although an uneasy calm has returned after national elections last year.

Two months of mass opposition protests in 2010 by “red shirt” supporters of ousted premier Thaksin Shinawatra sparked a deadly military crackdown that left about 90 people dead and nearly 1,900 wounded.

The unrest happened under a previous establishment-backed government that was swept from power last year by allies of Thaksin, whose sister Yingluck is now prime minister.

The organisers said they expected at least 500,000 protesters to attend, although the authorities estimate about 40,000-50,000 will turn out.

“This government ignores widespread disrespect of the monarchy and even supports the perpetrators. It is a puppet of Thaksin,” said Pitak Siam spokesman Vachara Riddhagni.

Thaksin, who made billions as a telecoms tycoon, is adored by many poor Thais for his populist policies while in power, but reviled by many in elite, military and palace circles who see him as authoritarian and a threat to the monarchy.

Observers say prosecutions for insulting the monarchy have surged since royalist generals toppled Thaksin in a coup in 2006. Many of those targeted are linked to the Red Shirt movement.