Human Rights Watch on Wednesday accused Emirati authorities of making a "mockery of justice" over the trial of 57 Bangladeshis who received lengthy prison sentences for protesting in the Gulf country.
The United Arab Emirates, a federation of seven sheikhdoms where demonstrations are banned, issued the verdict on Sunday after a swift investigation.
An Abu Dhabi court sentenced three Bangladeshis to life imprisonment and the others to jail terms of 10 to 11 years for taking part in protests against their government across the UAE on Friday.
The New York-based HRW criticised the "abusively fast judicial proceedings", saying they raised "serious concerns about fairness and due process".
Joey Shea, HRW's UAE researcher, said the sentences made "a mockery of justice".
"There is no way defendants can receive a fair trial when the investigation was launched and completed, trial commenced, and verdict rendered in less than 48 hours," she added.
UAE authorities provided few details about the protests, but HRW said videos it verified showed large demonstrations across several emirates, including Abu Dhabi and Dubai.
One video recorded near Dubai Mall showed "hundreds, possibly thousands, of protesters gathered on the road replicating slogans raised by the students in Bangladesh," HRW said.
Protests have swept Bangladesh this month against a quota system for civil service jobs that critics say benefits supporters of autocratic Prime Minister Sheikh Hasina.
Near-daily marches in the South Asian country escalated last week into civil unrest, leaving at least 186 people dead, according to an AFP count of victims reported by police and hospitals.
Bangladeshis form the third largest expatriate group in the United Arab Emirates, after Pakistanis and Indians, according to the UAE foreign ministry.
The oil-rich Gulf state bans unauthorised protests and prohibits criticism of rulers or speech that is deemed to create or encourage social unrest.
Defamation, as well as verbal and written insults, whether published or made in private, are punishable by law.
The country's penal code also criminalises offending foreign states or jeopardising ties with them.