Hamza Kashgari was arrested after arriving at Kuala Lumpur International Airport on Thursday and a police spokesman said was still being quizzed.
Kashgari fled Saudi Arabia after making comments on the microblogging site deemed insulting to the Prophet Muhammad, which fuelled a surge of outrage.
Insulting the prophet is considered blasphemous in Islam and is a crime punishable by death in Saudi Arabia.
Human Rights Watch senior Middle East researcher Christoph Wilcke said Malaysia should not be “complicit in sealing Kashgari’s fate by sending him back”, where he would be unlikely to face a fair trial.
“Saudi clerics have already made up their mind that Kashgari is an apostate who must face punishment,” he added.
“Malaysia should save him from any travesties of justice and allow him to seek safety in a country of his choice,” he said.
Rights activist S Arulchelvan of Suaram said Malaysia should not deport Kashgari but instead allow the United Nations refugee agency to investigate the issue.
Fadiah Nadwa Fikri, a spokeswoman for Malaysian activist group Lawyers for Liberty, said Kashgari was a blogger who had decried the “oppression of women”.
“This is again a violation of freedom of expression. He has every right of making comments and so on without being persecuted,” she told AFP.
“Malaysia should give asylum to him. But instead they are conspiring with the Saudi government. It’s abhorrent.”
Amnesty International had previously called for Kashgari’s immediate and unconditional release, saying he faced possible execution if he was returned to Saudi Arabia and his comments were ruled to amount to apostasy.
Malaysia and Saudi Arabia do not have a formal extradition treaty but have close ties as fellow Muslim countries.
Tweet sparks thousands of responses
A Malaysian Home Ministry official who asked to remain unidentified had said Kashgari could be extradited under other bilateral security agreements. Malaysia has in the past summarily deported people it considers undesirable.
Kashgari’s controversial tweet sparked tens of thousands of responses, according to an online service that tracks Twitter postings in the Arab world.
He tweeted: “I have loved things about you and I have hated things about you and there is a lot I don’t understand about you.
“I will not pray for you.”
Kashgari has apologised over the affair but that has not stemmed calls for his head.
A committee of top clerics branded him an “infidel” and demanded he be tried in an Islamic court, while a Facebook page entitled “The Saudi people demand Hamza Kashgari’s execution” has attracted thousands of followers.
The police spokesman, speaking on condition of anonymity, told AFP on Saturday that Kashgari was still in Malaysia and police were taking statements from him.
The police official said “a lot of red-tape” was involved in this case.
“Honestly I don’t know. It is subject to investigations and it also involves the government,” he said when asked if Kashgari would be sent back to Saudi.
Malaysia’s state news agency Bernama previously said he had been detained by the Muslim-majority country “for allegedly insulting Islam and the Prophet Muhammad”.
Police initially said that Kashgari was held following a request made by Interpol after the Saudis applied for it but an Interpol spokesman denied any involvement in the arrest, saying it was a matter between the two nations.
1:52PM Feb 11, 2012