Bangkok, Thailand (CNN) -- Tens of thousands of demonstrators on Tuesday continued anti-government protests in Bangkok intended to drive Thailand's Prime Minister out of office.
The protesters have laid siege to major intersections in Thailand's large and hectic capital city. At their peak on Monday evening, they numbered as many as 170,000, said Lt. Gen. Paradon Pattanathabut, the nation's security chief.
But their numbers have since declined to around 20,000 by Tuesday morning, Paradon said, as demonstrators returned to their homes in the Bangkok area and went to back to their jobs.
Their ranks may swell again by the evening after people finish work, he said.
The protesters, who say they want Thailand's political system overhauled instead of new elections scheduled for next month, occupied seven main intersections and blocked one government office on Monday.
Groups of them marched to several government buildings on Tuesday, including the labor, commerce and foreign ministries. In each case, the protesters entered the offices for a short period and then left -- a form of symbolic occupation.
Their activities are all part of an effort dubbed "Bangkok shutdown." It's orchestrated by the People's Democratic Reform Committee (PDRC) protest group, led by Suthep Thaugsuban, a former deputy prime minister for the opposition Democrat Party.
The government has offered talks with protesters and other concerned parties to discuss a way out of the impasse and the possibility of postponing the election. But Suthep's group has rejected the offer.
On Monday -- Day 1 -- students stayed at home as 140 schools were closed. At some of the intersections in the central business district, protesters stopped cars from passing blockades.
By Tuesday, most of the schools had reopened and the streets were busier. But the intersections occupied by protesters remained partially blocked.
Many people used alternative routes or means of transportation to reach their destinations.
The PDRC distanced itself from a group of protesters who threatened to shut down the stock exchange and an air traffic control tower at one of Bangkok's airports.
"We will stick with peaceful means to achieve our goal to reform," said Akanat Prompan, a PDRC spokesman. "We are trying to limit any possible damages to general public and businesses."
Police have also pledged to avoid using violence to deal with the protests.
Thailand is still scarred by the crackdown on anti-government demonstrators in 2010 that left about 90 people dead.
About 20,000 security personnel have been deployed to keep watch throughout the city. But so far, the shutdown has gone without serious incident.
Though many areas of the city are unaffected, several of the rally sites are in popular tourist areas.
Rights groups and others have called on Thai authorities and anti-government protesters to respect human rights and avoid violence during the mass demonstrations.
Since the anti-government protests began in November, eight people have died and 470 have been injured, authorities said.
"The situation in Thailand is tense, volatile and unpredictable," Isabelle Arradon, Amnesty International's Asia-Pacific deputy director, said last week. "There is a real risk of loss of life and injury unless human rights are fully respected."
U.N. Secretary General Ban Ki-moon said Friday in New York that he had spoken by telephone with Prime Minister Yingluck Shinawatra and opposition leader Abhisit Vejjajiva over the past three days "in an effort to help them bridge their differences."
Abhisit has denied being a member of the PDRC but has appeared on stage and among the crowds at some of their demonstrations.
In a bid to cool tensions, Yingluck dissolved the nation's parliament in December and called for new elections to be held on February 2.
But the move has done little to appease protesters. They have called on the Prime Minister to step down from her caretaker position and be replaced by an unelected "people's council," which would see through electoral and political reforms.
The national Election Commission has urged the government to postpone elections amid the continuing unrest. On Wednesday, Yingluck will meet with protest leaders and election commission officials to discuss whether to postpone, her office said.
But Akanat of the PDRC said Yingluck's offer of talks wasn't an answer to the problems.
The protesters want to see changes to Thailand's political system enacted before elections take place, he said, and the demonastrations will continue until they achieve that goal.
The U.S. government supports "a democratic process to resolve the ongoing political tensions in Thailand," Marie Harf, a State Department spokeswoman, said Monday.
"We also continue to urge all sides to refrain from violence, exercise restraint, and respect the rule of law," she said at a regular news briefing. "And we do, I would note, applaud the restraint shown thus far by government authorities in this regard."
Dozens of countries have issued travel advisories amid fears the tensions could erupt into violence.
The U.S. Embassy in Bangkok has urged U.S. citizens to avoid large gatherings in the city and to ensure they have a stock of cash and essential items in case the situation deteriorates.
"While protests have been generally peaceful over the last two months, some have resulted in injury and death," its online warning said. "Even demonstrations that are meant to be peaceful can turn confrontational, and can escalate into violence without warning."
The protest group has said that it will allow ambulances to pass along the roads it blocks, and that it will not block access to airports and public transportation.
Protest leaders have said they want to rid Thailand of the influence of former Prime Minister Thaksin Shinawatra, the older brother of Yingluck.
That's an ambitious goal in a country where every election since 2001 has been won by parties affiliated with Thaksin, a billionaire who built his political success on populist policies that appealed to Thailand's rural heartland.
Thaksin was ousted in a military coup in 2006 and has spent most of the time since then in exile overseas. If he returns, he risks a two-year prison sentence on a corruption conviction, which he says was politically motivated.
The recent protests in Bangkok were prompted by a botched attempt by Yingluck's government to pass an amnesty bill that would have opened the door for her brother's return.
That move added fuel for critics who accuse her of being nothing more than her brother's puppet, an allegation she has repeatedly denied.
Opposition to Thaksin and Yingluck is strongest among the urban elites and middle class, particularly in Bangkok.
Thaksin's traditional support comes from the populous rural areas of north and northeast Thailand.
His supporters, known as "red shirts," support the holding of elections on February 2.