Bangkok, Thailand (CNN) -- Thailand's red-shirted anti-government protesters returned to the streets of Bangkok Sunday for their first demonstration since a state of emergency was lifted last month.
Police said up to 30,000 opposition supporters descended on the area they occupied during the height of the protests last year. Sunday's "Red Shirt" demonstrators -- so named for the color of their clothing -- demanded a thorough investigation of a deadly government crackdown in May, along with the release of protest leaders, some of whom have been held in jail on terrorism charges for months.
Sunday's demonstration was largely peaceful, a police spokesman told CNN.
But Red Shirt organizers say they plan to hold regular demonstrations twice a month until their demands are met.
Between March and May of 2010, thousands of opposition protesters occupied parts of the shopping district in central Bangkok. For the most part, the Red Shirts were supporters of former Prime Minister Thaksin Shinawatra, who was ousted in a bloodless military coup in 2006. They wanted the resignation of Prime Minister Abhisit Vejjajiva and a new general election.
But their protests came to a bloody end in May. Government troops cracked down and drove them out of their positions in the Thai capital. Ninety-one people died and at least 1,500 others were injured in the clashes, which saw intense street battles between protesters and government troops. More than 30 buildings -- including a bank, a police station, a local television station and Thailand's biggest shopping mall -- were set on fire.
Amid the unrest, the Thai government imposed a state of emergency that put the military in charge of security. It lasted seven months and was only lifted in December. The prime minister has promised to hold a new election before the end of 2011.
CNN's Kocha Olarn contributed to this report.