Her calls were echoed by the EU's special envoy to Myanmar, who said the new charges brought against Aung San Suu Kyi were without foundation.
"There is no justification" for the decision to charge her with breaching the terms of her house arrest and put her on trial next Monday, Piero Fassino told Italy's Channel 5 television on Thursday.
Fassino said the international community should use "every possible means to press for the release of Aung San Suu Kyi" as well as "the 2,000 other political prisoners who are held in Burmese jails".
The opposition leader, who was recently treated for dehydration and low blood pressure, was on Thursday taken by police from her home in Yangon, where she has been under house arrest, to Insein prison on the outskirts of the former capital.
She was charged with breaking the terms of her house arrest and faces up to five more years' imprisonment over the intrusion of an American who allegedly swam across a lake and entered her home last week, her lawyer, Kyi Win, said.
Kyi Win said the trial would start on May 18.
The 63-year-old has been detained without trial for more than 13 of the last 20 years, with the military refusing to recognise her National League for Democracy's (NLD) landslide victory in the country's last elections in 1990.
Critics have denounced the latest charges, saying any trial could be used to justify another extension of her house arrest which officially expires on May 27.
|Myanmar police say Yettaw met Aung San Suu Kyi during his two-day stay at her home [EPA]
The EU's Czech presidency highlighted the timing of the move in a statement from Brussels.
"It is especially striking that these events practically coincide with the expiry of her house arrest," it said.
The statement stressed that the UN has deemed the terms of her detention to be in violation of international and national law.
"The EU strongly urges Myanmar's authorities to release Aung San Suu Kyi and engage in an inclusive process of national reconciliation, which is essential for setting Myanmar on a genuine path to stability and prosperity," it added.
Zin Linn, the director of the National Coalition Government of the Union of Burma, a pro-democracy group that supports Aung San Suu Kyi, told Al Jazeera that there was an "ulterior" motive to the trial.
"They are finding fault with her to extend her detention because they didn't allow her to participate in the election, that is their main intention," he said, calling the military's move "very cunning and crooked".
"She was under house arrest. Any security measure was taken by the authorities, so whoever [enters] into the compound of a resident, the responsibility is upon the authorities, not upon her," he added.
The military government has in the past found various reasons to extend her periods of house arrest.
The charges apparently stem from an incident in which an American man, John William Yettaw, was arrested last week for allegedly swimming across a lake to secretly enter Aung San Suu Kyi's home in Yangon and stay there for two days.
Myanmar's state-run newspapers reported last week that Yettaw, 53, swam on the night of May 3 to her lakeside home, "secretly entered the house and stayed there" for two nights.
He then swam away on May 5 before being arrested the next morning.
Myanmar official sources said the man had succeeded in meeting Aung San Suu Kyi during his time at the house.
His motives remain unclear, but Kyi Win said Yettaw tried to meet Aung San Suu Kyi last year, but was told to leave and the incident was reported to the authorities.
The opposition leader again told him to leave, but this time he refused, Kyi Win said.
"He said he was so tired and wanted to rest, but she pleaded with him. Then he slept overnight on the ground floor," Kyi Win told the Democratic Voice of Burma (DVB) after he was allowed to meet Aung San Suu Kyi on Wednesday.
Myanmar citizens are required by law to notify local officials about any overnight visitors who are not family members.
The law also states that foreigners are not allowed to spend the night at a local's home.
According to the US Campaign for Burma, a US-based lobby group opposed to military rule in Myanmar, Aung San Suu Kyi, her two helpers, her personal doctor Tin Myo Win, and Yettaw would all be tried together.
The two helpers, Khin Khin Win, 65, and her daughter Win Ma Ma, 41, have lived with Aung San Suu Kyi since the start of her latest detention in 2003.
Tin Myo Win was arrested without explanation last week, a day after Yettaw was taken into custody.