Thailand's Senate defeated an amnesty bill on Monday that could have led to the return from exile of deposed former Prime Minister Thaksin Shinawatra, but opponents of the bill vowed to continue their protests against the government.

The main opposition Democrat Party called for civil disobedience and a three-day nationwide strike beginning Wednesday in what has turned into a campaign to bring down the government led by Thaksin's sister, Prime Minister Yingluck Shinawatra.

Critics say the amnesty bill was an attempt by the government to whitewash Thaksin's alleged crimes and pave the way for his return. Thaksin, a highly divisive figure, fled the country in 2008 to escape a two-year jail term on a corruption charge.

The Senate voted 141-0 late Monday to reject the bill after the ruling party withdrew its support. Yingluck has pledged that the bill will not be revived, although the more-powerful lower house can legally pass legislation without Senate approval after a 180-day wait.

Demonstrations against the bill have spread since it was passed by the lower house on Nov. 1. Their target has shifted in recent days to the government, threatening to end Thailand's two years of relative political calm since Yingluck took office.

Before that, Thailand had been rocked by years of often-violent political conflicts that led to Thaksin's ouster in a 2006 military coup over allegations of corruption and disrespect for King Bhumibol Adulyadej. His ouster came after widespread demonstrations against him in Bangkok.

Disputes between Thaksin's supporters and opponents arouse fierce passions which culminated in a 2010 military crackdown on Thaksin supporters that left about 90 people dead.

Paving the way for Thaksin's return has been an unspoken priority of Yingluck's government, which won an absolute parliamentary majority in 2011 elections due largely to Thaksin's popularity in rural areas and among the urban poor, who benefited from his government's populist programs.

Since the amnesty bill was passed by the lower house, the bill has set off demonstrations in Bangkok by both pro- and anti-government supporters.

On Monday, tens of thousands of protesters rallied in several parts of the capital. Nearly 7,000 police officers were deployed around Parliament in the city's historic district, near the main protest site.

On Monday evening, the Democrat Party called for a three-day strike by businesses and schools to allow people to join the protests; a withholding of taxes that allegedly go for corruption; the display of the national flag; and the blowing of whistles, which have become a tool of protest, near government leaders.

Democrat deputy leader Suthep Thaugsuban and eight other party lawmakers said they were resigning their parliamentary seats to lead the anti-government campaign. The resignations are a legal shield for the party, which could face dissolution if its lawmakers were found guilty of trying to unlawfully unseat a constitutional government.

Although the protests have drawn a high profile and are the strongest ever against Yingluck's government, it was unclear if they are sustainable, especially in view of the overwhelming support that Yingluck's government has in Parliament.

The original draft of the bill did not extend amnesty to the leaders of both the pro- and anti-Thaksin groups, but a House committee in mid-October suddenly changed the bill to include both. The last-minute change led to criticism that it was planned all along to encompass Thaksin.

The Senate debate coincided with another highly charged ruling Monday by the U.N.'s highest court on a territorial dispute with Cambodia.

The International Court of Justice in The Hague ruled that Cambodia has sovereignty over a disputed promontory around a 1,000-year-old temple that has fueled nationalist passions on both sides for decades.  However, the ruling did little more than preserve the status quo, and the government claimed that it lost no ground in the longstanding dispute.

The government was concerned that if Thailand lost the case it would be used by protest leaders to stir up its critics' passions. (AP)