An Australian senator on a fact-finding mission to Malaysia says he has been refused entry because authorities consider him a "security risk".
Nick Xenophon was detained at Kuala Lumpur airport on Saturday morning and will be deported back to Australia, correspondents say.
He was part of an Australian delegation scheduled to meet Malaysian officials to discuss forthcoming elections, reports the BBC.
Xenophon has been an outspoken critic of human rights in Malaysia.
The independent senator from South Australia was taken into custody at Kuala Lumpur airport on Saturday morning and detained apparently under Malaysia's national security laws, the BBC's Nick Bryant reports from Sydney.
Immigration officials were polite but acting under orders "from above", Xenophon told reporters.
"I was told I am a security risk and I can't be allowed into the country. It's bizarre and extraordinary," the senator said.
"I've been here before [and] I've made statements about the state of Malaysian democracy previously. But on this occasion clearly someone high up in the Malaysian government doesn't want me here."
Authorities advised Xenophon he would deported on the next available flight to Australia.
"They have basically told me I am an enemy of the state. They are trying to get me on the next plane out of here and back home," he told the Australian Sunday Mail newspaper by phone.
Xenophon had flown to Malaysia as part of an Australian parliamentary fact-finding mission to assess whether forthcoming elections would be free and fair, our correspondent says.
The delegation was scheduled to hold talks with several Malaysian parties, including opposition leader Anwar Ibrahim and officials from the election commission.
A regular visitor to the country, Xenophon last year observed the trial of Ibrahim, who was acquitted on sodomy charges.
Xenophon was also caught up in anti-government protests and reportedly tear-gassed by riot police at a demonstration in Kuala Lumpur demanding democratic reforms in April last year.
Australian Foreign Minister Bob Carr said his government was seeking Xenophon's immediate release and had raised the issue with the Malaysian government.
"Senator Xenophon's detention is a surprising and disappointing act from a country with which Australia routinely maintains strong diplomatic relations," Carr said.
"Our High Commissioner Miles Kupa has now made direct contact with Senator Xenophon at the airport and is seeking his release."
Other members of the Australian delegation have now pulled out, our correspondent says.
Malaysian authorities have not commented on the senator's arrest.