Anti-amnesty rally photos by Bangkok Post photographers
Suthep Thaugsuban, the protest leader, made the announcement after leading thousands of demonstrators to pay respects to the deaths of protesters and security authorities killed in a clash on the street rallies on April 10, 2010.
The Democrat MP for Surat Thani said the new strategy was to step up measures to press on the government to drop the amnesty bill.
"We have decided to accelerate our fight by occupying Ratchadamnoen Avenue," Mr Suthep said after observing a minute of silence to the victims including Gen Romklao Thuwatham, who was brutally killed by the "men in black" at Khok Wua Intersection on that night.
He said he made the new decision after calls by protesters who wanted to see the Democrat-led rally increase pressure on the government.
The new rally site of the opposition party in Phra Nakhon district is under enforcement of the Internal Security Act, which also covers Dusit and Pomprap Sattruphai districts since Oct 9.
Deputy Prime Minister Pracha Promnok said before the Democrats had changed the plan that the government is keeping only the three districts under the act and remained confident of keeping the protesters in check.
Pol Gen Adul Saengsingkaew, the national police chief who directs the Centre for the Administration of Peace and Order, said security agencies are assessing the situation after protests were spread to other locations.
Video by Pattarapong Charpattarasill
Meanwhile, Prime Minister Yingluck Shinawatra has pleaded for all sides to forgive one another and allow the country to step forward.
Ms Yingluck made the plea for mutual forgiveness when a group of relatives of those killed in political violence called on her at Government House to give her moral support.
She expressed sympathy for the relatives of the victims, who she said had sufferred a great loss.
"Only if we adhere to the principle of forgiveness and reconciliation can the country move forward. Amicable talks can lead to a way out of the impasse," Ms Yingluck said.
The prime minister said she believed many people were worried by the opposition to the amnesty bill for fear of a recurrence of past violence.
"Which ever way we may take, it won't satisfy everyone," she said.
Asked about the growing number of people opposing the amended amnesty bill, Ms Yingluck said the government is duty-bound to take care of them and she believed the protests would be peaceful.
Asked whether she still believed the bill would bring about reconciliation, the prime minister said: "We have to forgive one another."
Without forgiveness, everything would be at a standstill, she said.
Video by Thiti Wannamontha