Hundreds of Thai protesters have gathered in the Thai capital, Bangkok, to rally against the government and divisive former Prime Minister Thaksin Shinawatra, who lives in self-imposed exile.
Brandishing Thai national flags as well as the yellow emblem of the country's monarchy, demonstrators milled around restaurant carts and memorabilia stalls set up at the protest site in a central Bangkok park.
Organisers of the self-styled "People's Army" rally - a coalition of ultra-royalist and nationalist groups - adressed the crowd from a stage, calling for the end of the current government and slamming its self-exiled figurehead Thaksin.
"It is time for Thai people who love the country to unite and become a people's army to overthrow the Thaksin regime," one of the group's key leaders, retired general Preecha Iamsuwan, told the rally.
Despite initial concerns over the potential for unrest in Bangkok, which has suffered several bouts of political violence in recent years, security forces kept a low profile at the event.
Police, who have said they are authorised to use water cannon, tear gas and rubber bullets if violence erupts, put the number of demonstrators at 1,500 with up to 4,000 expected by late Sunday.
The police had brought in reinforcement ahead of the protests, against an amnesty law that critics says is aimed at helping the exiled former Prime Minister return home.
Eleven police companies were deployed at different locations in the three districts, according to local media.
Prime Minister Yingluck Shinawatra, Thaksin's sister, on Saturday expressed "worry that the rally could lead to violence".
Sunday's protesters are targeting the government-backed bill, due to enter parliament on August 7, which proposes an amnesty for those involved in political violence since a 2006 coup that toppled Thaksin.
The young Thai Prime Minister in a televised address on Friday called for a dialogue among different political stakeholders. Her government has been pushing for political reconciliation that has eluded this South Asian nation.
The Thai government has already invoked the Internal Security Act to control the protests, which could go on for several days.
More than 1,600 police were deployed on Saturday to protect key government buildings, while thousands more were put on standby.
Mass demonstrations, often involving bloodshed, have become a recurrent feature of Thailand's turbulent politics in recent years, with ultra-royalist nationalist "Yellow Shirts" supporters of the opposition Democrat Party, and the pro-Thaksin "Red Shirt" foes both taking to the streets.
In 2010, two months of Red Shirt protest against a previous government brought much of Bangkok to a standstill and culminated in a bloody military crackdown that left about 90 people dead and another 1,900 injured.
The country has been riven by political tensions since the overthrow of Thaksin, a deeply divisive figure who lives abroad but still draws loyalty among the kingdom's poor, rural working class.