BANGKOK (AP) -- Protesters calling for Thai Prime Minister Yingluck Shinawatra to step down rallied in the heart of Bangkok on Saturday, clashing with police in the first major demonstration against the government since it came to power last year.
Organizers had spoken of mobilizing hundreds of thousands of supporters. But only around 10,000 turned up, and by dusk the leaders called the rally off.
Nevertheless, the tense gathering served as a reminder that the simmering political divisions unleashed after the nation's 2006 army coup have not gone away. The coup toppled Yingluck's brother, Thaksin Shinawatra, triggering years of instability and mass-protests that have shaken Bangkok.
Saturday's rally was organized by a royalist group calling itself "Pitak Siam" -- or "Protect Thailand." Led by retired army Gen. Boonlert Kaewprasit, the group accuses Yingluck's administration of corruption, ignoring insults to the monarchy and being a puppet of Thaksin.
Yingluck took the group's threats seriously and accused them of trying to topple her government, which came to power in mid-2011 after winning a landslide electoral victory. Concerned about possible violence, Yingluck deployed nearly 17,000 police and invoked a special security law to give them extra powers.
Although the rally site itself was peaceful, protesters on a nearby street tried to break through a concrete barricade guarded by thick lines of hundreds riot police with shields, at one point ramming a truck into it. Both demonstrators and police hurled tear gas canisters at each other.
Police spokesman Maj. Gen. Piya Utayo said five officers were injured in the skirmishes, two of them seriously. He said 130 demonstrators were detained, some of them carrying knives and bullets. Local hospital staff said they treated 45 people and most had inhaled tear gas.
Speaking from the rally's central stage on Saturday, Boonlert vowed the demonstration would remain peaceful. But he said: "I promise that Pitak Siam will succeed in driving this government out."
He then led the crowd in a chant: "Yingluck, get out! Yingluck, get out!"
The rally was held at Bangkok's Royal Plaza, a public space near Parliament that has been used by protesters in the past.
Police allowed protesters into the site, and two roads leading to it were open. But in an effort to control access, they blocked roads on another street leading to Royal Plaza. Protesters tried to break through the barriers in the morning, cutting through more than half a dozen rings of barbed wire. They clashed with police in the area at least twice on Saturday, and some carried their own tear gas.
While Pitak Siam is a newcomer to Thailand's protest scene, it is linked to the well-known "Yellow Shirt" protesters, whose rallies led to Thaksin's overthrow. The same movement later toppled a Thaksin-allied elected government after occupying and shutting down Bangkok's two airports for a week in 2008.
Thaksin remains an intensively divisive figure in Thai politics. The Yellow Shirts and their allies say he is corrupt and accuse him of seeking to undermine the popular constitutional monarch -- charges Thaksin denies.
On Thursday, Yingluck's Cabinet invoked an Internal Security Act in three Bangkok districts around the protest site. The act allows authorities to close roads, impose curfews and ban use of electronic devices in designated areas.
Since then, police have closed roads around Yingluck's office and Government House, and boosted security at the homes of senior officials, including the prime minister.
In a nationally televised address explaining the move, Yingluck had said protest leaders "seek to overthrow an elected government and democratic rule ... and there is evidence that violence may be used to achieve those ends."
Analysts said they did not view the protest as an immediate threat to Yingluck's government, but were watching it closely.
"Anytime you have tens of thousands of people converging, assembling in a central Bangkok location, it becomes a government stability concern," said Thitinan Pongsudhirak, a political scientist at Bangkok's Chulalongkorn University.
But he added: "I think it's a serious concern more than a serious threat."
Boonlert, the protest group's leader, is best known for his role as president of the Thailand Boxing Association. His name is unfamiliar in the anti-Thaksin protest movement, but his message appears to have resonated with Yellow Shirt supporters who have laid low in recent years after Yingluck's party won the last elections.
Thailand has been gripped by bouts of political instability since 2006, with Thaksin's supporters and opponents taking turns to spar over who has the right to rule the country.
The most violent episode came in 2010, when Thaksin's "Red Shirt" supporters led a two-month occupation of central Bangkok to demand the resignation of an anti-Thaksin government. The protests led to a military crackdown that left at least 91 people dead and more than 1,700 injured.
Thaksin has lived in self-imposed exile since 2008, when he jumped bail to evade a corruption conviction and two-year jail term. He retains huge popularity among the rural poor, who want to see him pardoned and returned to power. But he is reviled by the urban elite and educated middle class, who see him as authoritarian and a threat to the monarchy.
Buoyed by Thaksin's political machine, Yingluck was elected by a landslide victory in August 2011. She initially was criticized for her lack of political experience -- she was an executive in Shinawatra family businesses -- but has won praise for leading the country through one of its longest peaceful periods in recent years.
Associated Press photographer Sakchai Lalitkanjanakul contributed to this report.