Mu Sochua and Sam Rainsy, the main opposition leader, were scheduled to return to Cambodia on Saturday.

Malaysia has detained the deputy chief of Cambodia‘s banned opposition party, Mu Sochua, after Phnom Penh accused her and other self-exiled opposition figures of seeking to return home to stage a coup against longtime leader Hun Sen.

Malaysian Prime Minister Mahathir Mohamad indicated on Thursday that Sochua would not be turned over to Cambodia but would instead be deported to an as-yet-undetermined third country.

The detention came as Sam Rainsy, the founder of the opposition party, prepared to fly from Paris to Bangkok, vowing to return to Cambodia on Saturday to lead demonstrations against the one-party rule of Prime Minister Hun Sen.

Sochua, 65, is one of several opposition leaders who fled from Cambodia fearing arrest and are now seeking to return with Rainsy to rally support for their cause.

“Malaysia’s immigration’s action to detain Mu Sochua at #KLIA is absolutely ludicrous & unacceptable. She’s done nothing wrong and should be immediately released, and allowed to undertake the consultations she planned with the #Malaysia government and civil society groups" @hrw pic.twitter.com/VDlQ8PY23g — Phil Robertson (@Reaproy) November 7, 2019

She flew into Kuala Lumpur on her United States passport and was being detained at the airport.

Before boarding her flight from Jakarta to Kuala Lumpur on Wednesday night, Al Jazeera asked Sochua if she was concerned about her safety, and she replied: “If we were to be concerned we wouldn’t get to the goal”.

There was no response to a follow-up message Al Jazeera sent to Sochua on Thursday morning.

Speaking to reporters in Malaysia’s Putrajaya, Mahathir said his country was bound by its principle of non-interference in neighbours’ affairs in the Association of Southeast Asian Nations (ASEAN).

“We do not want to let them to use Malaysia as a base for struggle in other countries,” Mahathir said. “We wanted to deport her … now we are trying to find any country that can take her.”

‘Unconditional release’

The US was ware of the situation, a US government spokesman said. He would not comment further due to privacy restrictions.

In late October, Sochua was also denied entry to Thailand and was sent back to Malaysia.

In a statement issued on Thursday, the ASEAN Parliamentarians for Human Rights (APHR) called for the “immediate and unconditional release” of Sochua.

“The decision to detain her is a complete disregard for ASEAN’s stated commitment to democracy and human rights. We all know that any attempts to block Cambodian opposition members from returning to their countries is solely based on political grounds and is a blatant attempt to silence their voices,” said Kasit Piromya, former Thailand MP and Board Member of APHR.

The news of Sochua’s detention comes just a day after Malaysian authorities acknowledged on Wednesday that they have detained two Cambodian opposition activists late on Tuesday.

Cambodia has arrested at least 48 opposition activists this year for allegedly plotting to overthrow the government before the planned return from self-exile of Rainsy, founder of the dissolved CNRP, on Saturday.

Hun Sen’s government deployed troops along its borders in response to Rainsy’s announcement of his planned return.

Rainsy fled to France four years ago following a conviction for criminal defamation in which he was ordered to pay $1m in compensation. He also faces a five-year prison sentence in a separate case.

He has previously said it was legitimate to seek to topple Hun Sen because the prime minister has created a one-party state and was not prepared to hold free and fair elections.

On Wednesday, Thai Prime Minister Prayuth Chan-ocha said that Rainsy would not be allowed to enter Thailand on his way to Cambodia.

With additional reporting by Leonie Kijewski in Phnom Penh