The protesters want the government to resign and call elections
Thailand's ousted former leader Thaksin Shinawatra has addressed a big crowd of supporters in Bangkok by telephone, urging them to continue protesting.
The crowd cheered as Mr Thaksin, who lives in exile in Dubai, criticised the policies of the current government.
He complained of being lonely and told the crowd not to leave him "dying in the desert", promising to "work for the people" if he could return.
Police estimated more than 25,000 were at the rally - the largest since April.
Prime Minister Abhisit Vejjajiva called a state of emergency in April as the rallies by red-shirted protesters threatened to destabilise his government.
The protest leaders eventually called off their action after days of rioting and clashes with security forces left at least two people dead and more than 100 injured.
Mr Thaksin told his supporters they had gathered because they wanted to see "true democracy".
Royalists saw Mr Thaksin's popularity as a threat to the monarchy
"We loathe injustice. We loathe double standards. We're here to say if you want us to stop, then return justice and true democracy," he said.
To roars of approval, he said the current government was good for three things: "Borrowing, hiking taxes and hounding Thaksin."
He also entertained the crowd with songs, and begged them to find a way for him to return to Thailand.
"Why do you have to leave me dying in the desert when I can work for our country?" he said.
"I'm a grateful person. When I'm back, I'll work for the people right away."
Mr Thaksin has spent much of his time abroad since he was deposed in a military coup in 2006.
He was convicted of corruption in 2008 - a prosecution he says was politically motivated - and faces jail if he returns to Thailand.
Yellow vs red
Mr Abhisit came to power last December after previous Thaksin-supporting governments were brought down by a concerted street protest by yellow-shirted demonstrators.
He was eventually chosen as leader after several MPs who had previously backed Mr Thaksin were persuaded to change sides.
Analysts say the rift in Thai society - symbolised by the red and yellow shirts - remains strong.
Many Thais in rural areas support Mr Thaksin and ally themselves with the red-shirt cause.
The "yellow shirts" draw their support from Bangkok's urban elite, the middle classes and the conservative royalists.