Rights groups have blasted Malaysia for reportedly deporting Singaporean activist Han Hui Hui on Sunday.

According to International Federation for Human Rights (FIDH) and Suaram, Han was supposed to attend a human rights workshop in Kuala Lumpur.

“Malaysian authorities treated Han as if she were a dangerous criminal.

"The travel ban imposed on Han limits her rights to freedom of expression and peaceful assembly and must be lifted immediately,” said FIDH president Dimitris Christopoulos in a statement jointly issued by FIDH and Suaram.

The groups claimed Immigration Department officers at Kuala Lumpur International Airport prevented Han from clearing Immigration, and detained her for several hours.

"During the detention, plainclothes officers informed Han that she was blacklisted from entering Malaysia," wrote FIDH and Suaram.

The groups said Han had been invited to attend the Regional Youth Exchange Program organised by Suaram from 19 to 23 June in Kuala Lumpur.

“It is a sad state of affairs when the Malaysian government declares an activist persona non grata and prevents her from attending a human rights workshop.

"Han must be removed from the blacklist immediately and allowed to engage in peaceful human rights activities that are beneficial to Malaysians,” said Suaram executive director Sevan Doraisamy.

'No problems before'

According to the NGOs, she had not encountered problems entering Malaysia in her five previous visits from April 2015 to this March.

She has been banned under Article 8(3)K of the 1959/63 Immigration Act, which allows Immigration to bar any person who is deemed by the home minister to be “an undesirable immigrant” from entering the country.

Han, who has actively campaigned to promote government transparency and accountability in Singapore, has previously been detained in the island state.

According to FIDH and Suaram, she spent several hours in the Singapore State Courts lock-up on charges of causing a public nuisance under Article 290 of the Singaporean Criminal Code, over a peaceful demonstration she had organised in September 2014.