Colombo, Sri Lanka (CNN) -- Sri Lanka's opposition Tuesday called for nationwide protests over the "barbaric and extra-judicial" arrest of the country's former army chief, accusing President Mahinda Rajapaksa of undermining the country's democratic institutions.
Retired Gen. Sarath Fonseka, who ran against Rajapaksa in January's elections, was arrested Monday night on charges of conspiring to overthrow the government and assassinate his rival. And Rajapaksa announced Tuesday that he was dissolving the country's parliament, a step toward new parliamentary elections.
"We urge all those who believe in the need to keep democracy alive in Sri Lanka to join us and rally against this ruling junta and do whatever it takes to protect our motherland from destruction," the leaders of eight opposition parties said in a joint statement Tuesday. "In the past, Sarath Fonseka and his soldiers fought in the blood-drenched battlefields of this country to keep us safe. The time has come for us to rise up and return the favor."
In a separate statement, they called Fonseka's arrest a "barbaric and extra-judicial" attempt to punish the former general -- Sri Lanka's most decorated soldier -- for challenging Rajapaksa in January's election. Fonseka lost that vote by a wide margin, a result he has blamed on widespread fraud.
Both leaders are considered heroes for defeating the quarter-century revolt by the Tamil Tiger separatist movement in 2009. Opposition leaders said they would stage protests around the country, including one in Colombo's court district, on Wednesday to call for Fonseka's release.
The sharply worded opposition statement compared Rajapaksa to Ugandan strongman Idi Amin and said Sri Lankans were "still reeling from the shock of how far this government will go to exact revenge."
"We also call upon the service personnel to refrain from carrying out illegal orders, no matter who dispenses them, in a bid to do your part towards protecting what is left of democracy in this country," it added.
With lawmakers' five-year terms ending in April, Tuesday's presidential decree dissolving parliament is a step toward holding new legislative elections. Fonseka was discussing the upcoming campaigns with opposition leaders when he was arrested at his Colombo office Monday night, said Jayalath Jayawardena, a member of parliament from the pro-Fonseka United National Party.
Lakshman Hulugalle, director general of the Media Center for National Security, told reporters Tuesday that Fonseka faces a number of charges, including creating divisions in the military; divulging military secrets to opposition parties; attempting to overthrow the government; and involvement in an alleged attempt to assassinate Rajapaksa. The former general was arrested under a law that allows prosecutors to charge former officers in military courts up to six months after retirement, Hulugalle said.
Military spokesman Maj. Gen. Prasad Samarasinghe told reporters Fonseka was at a "comfortable apartment with television and other amenities" and that his family had been allowed to see him. And Jayawardena told CNN that Fonseka was being held at the country's navy headquarters in Colombo and that his wife and attorney were given access to him.
But Fonseka's wife Anoma said her requests to see her husband had been denied, and she has been unable to deliver medication for a lung ailment he suffers after sustaining injuries in a 2006 suicide bombing inside army headquarters. Anoma Fonseka said she has appealed to the International Committee of the Red Cross to get the medicine to her husband.
Opposition officials said they are looking into filing a case in the country's supreme court alleging the government had violated Fonseka's fundamental rights.
"This is not an arrest. This is an abduction," Mangala Samaraweera, a spokesman for Fonseka and a former foreign minister under Rajapaksa, told reporters Tuesday.
Opposition leaders said a group of about 150 soldiers, led by a major general, stormed the opposition meeting Monday night seized Fonseka. Rauff Hakeem, the leader of the Sri Lanka Muslim Congress, said Fonseka offered to surrender to police, but said, "This was not accepted."
"At least three times, the officer shouted orders to forcibly take charge of the retired general," Hakeem said. "The third time, some of the soldiers bundled him up from the upstairs of his office. I saw one of them hitting him."
Fonseka broke ranks with the Rajapaksa administration after he was elevated to the largely ceremonial post of chief of the defense staff in 2009. The move to the less-powerful position apparently came amid government fears that Fonseka was too powerful and could stage a coup.
During the campaign, Rajapaksa's supporters sought to disqualify Fonseka on the grounds that he was not registered to vote. Troops surrounded the hotel Fonseka used as his headquarters the day after the election, leading the former general to accuse his onetime ally of "ignoring the constitution to remain in power."
Fonseka has denied previous government accusations that he planned to overthrow the government or assassinate Rajapaksa. He has said in newspaper interviews in recent days that he feared being arrested on the night of the election.
January's vote was Sri Lanka's first peacetime election since 1983, when the Tigers launched a campaign aimed at creating a separate homeland for the country's ethnic Tamil minority. The movement controlled large parts of the island's north at the height of its power.
The conflict was blamed for 70,000-80,000 deaths before 2009, when government forces reclaimed the rebel-held territories and declared victory. They were blamed for the assassinations of Sri Lankan President Ranasinghe Premadasa in 1993 and Indian Prime Minister Rajiv Gandhi, who had sent Indian peacekeepers to Sri Lanka, in 1991.
CNN's Sara Sidner contributed to this report.