Protesters pour blood at the Thai prime minister's home
Thai protesters have hurled plastic bags filled with gallons of blood in a symbolic protest at the prime minister's house in Bangkok.
Security forces agreed to let a few of the red-shirted demonstrators splatter the blood outside the compound of Prime Minister Abhisit Vejajjiva.
They went on to picket the US embassy, accusing US intelligence of bugging deposed ex-PM Thaksin Shinawatra.
The opposition, many of whom back Mr Thaksin, want fresh polls.
Red-shirt leaders and government figures have insisted they are determined to keep the protests, the largest in recent years, peaceful.
The demonstrators say Mr Abhisit's government is illegitimate and should be dissolved.
Neither Mr Abhisit nor his family were at their home in the upmarket Bangkok suburb.
He has been staying at the headquarters of the 11th Infantry Battalion in the north of Bangkok since the protests began.
Police and troop reinforcements were drafted in at the last minute to the prime minister's house, sparking fears of a confrontation.
The government had said it would ban the protest, but once again a negotiated solution was found.
Several dozen demonstrators were allowed through the police cordon carrying plastic bottles filled with blood, which was poured into small plastic bags and then thrown at the home.
Government cleaners quickly went into action to mop up the blood on Tuesday.
There was criticism that the protest wasted a resource which could have been used to help the sick.
Several thousand of the demonstrators later gathered outside the American embassy in the Thai capital.
Some said they were there to tell the international community that their government was illegitimate.
But others said the US had accused Mr Thaksin of inciting violence after snooping on the billionaire former leader's phone calls.
The BBC's South East Asia correspondent Rachel Harvey says the protesters' numbers are dwindling, but the passion is undiminished and the demands as loud as ever.
A senior police officer said he estimated numbers had dropped from 100,000 to 90,000 people by Tuesday evening.
Reporters asked a protest leader, Veera Musikapong, what their next move would be, and he replied: "I want to know that myself," the Associated Press reported.
He said the group mapped strategy on a day-by-day basis.
2006: Yellow-shirts launch street protests to oust PM Thaksin Shinawatra
Sept 2006: Thaksin ousted in military coup
Dec 2007: Thaksin allies win first post-coup elections
Sept 2008: Yellow-shirts occupy Bangkok government buildings, clash with pro-Thaksin red-shirts
Nov 2008: Yellow-shirts occupy Bangkok's airports, forcing cancellation of hundreds of flights
Dec 2008: Thaksin-allied government falls, rival Abhisit Vejjajiva forms government
Apr 2009: Red-shirts storm Asean summit, clashes erupt in Bangkok
Mar 2010: Red-shirts launch protest aimed at bringing government down
On Tuesday, they poured human blood at the gates of Government House and, later, the headquarters of the Democrat Party.
Many thousands of protesters had lined up to donate their blood.
"The blood of the common people is mixing together to fight for democracy," said Natthawut Saikua, a red-shirt leader.
Tens of thousands of security forces remain on standby and army leaders say they plan to be flexible and gentle as the protests continue.
On Monday, Mr Abhisit rejected a demand from protesters to quit and call elections.
The stand-off is the latest in a deep political schism in the country, linked to the 2006 military coup which deposed former leader Thaksin Shinawatra.
A cabinet meeting scheduled for Tuesday was cancelled, and a parliamentary hearing stopped for lack of a quorum.
Both sides appeared to be making every effort to avoid confrontation.
The protesters say the present government was installed illegally after Mr Thaksin was ousted in a military coup in 2006, and two subsequent allied governments were deposed by court action.