Cambodian opposition leader Kem Sokha has been unexpectedly released from prison where he was awaiting trial on charges of treason.

Mr Sokha has been released on bail and it is not clear if the charges against him will be dropped.

He had been arrested in 2017 in a case widely seen as politically motivated.

His party was subsequently dissolved and with no political opposition left, the ruling party won a landslide election victory earlier this year.

The crackdown on the opposition sparked international condemnation and threats to withdraw aid from the country.

Mr Sokha had been accused of colluding with the US to conspire against the Cambodian government. If found guilty, would have faced up to 30 years in jail.

The politician was the head of the Cambodia National Rescue Party, seen as the only contender to the ruling party led by strongman Hun Sen, who has been in power for more than 30 years.

The party was outlawed in November 2017, allowing the ruling Cambodian People's Party (CPP) to win all seats in the July 2018 general election, making Cambodia a de facto one-party state.

Western countries and human rights organisations have described Mr Sokha's arrest as arbitrary, calling for his release.

After the July election, the EU said it was considering economic sanctions while the US said it considered placing visa restrictions on government officials.

Hun Sen, a former soldier in the Khmer Rouge regime who later opposed them, has been in power since 1985. He was installed by Vietnamese forces after they had ousted the genocidal regime.

He presided over a sustained period of rapid economic growth but has long been accused of using the courts and security forces to crush dissent and intimidate critics.