BANGKOK, Jan. 21 (CNA) - A banned Thai opposition politician, who is facing a criminal complaint of defaming the monarchy, defended on Thursday (Jan 21) his criticism of the government's COVID-19 vaccine strategy that relies on a company owned by King Maha Vajiralongkorn.

Thanathorn Juangroongruangkit this week accused the government of Prime Minister Prayut Chan-o-cha of mishandling the vaccine campaign, saying it was too reliant on Siam Bioscience and will be slow to protect the public.

The Thai company is owned by the Crown Property Bureau, the organisation that manages tens of billions of dollars in investment under the king's personal control.

Siam Bioscience agreed in October to manufacture AstraZeneca's COVID-19 vaccine and supply it domestically and across Southeast Asia.

The government has ordered 61 million doses of AstraZeneca's vaccine for its population, as well as 2 million doses of a vaccine made by China's Sinovac Biotech.

Thanathorn had alleged the AstraZeneca deal lacked transparency and Siam Bioscience was given an unfair advantage over other companies.

He said the government, by relying mostly on AstraZeneca instead of negotiating multiple deals, has slowed the rollout of vaccines for Thais to June, while other countries have already begun to vaccinate their populations.

Both AstraZeneca and Siam Bioscience declined to comment on Thanathorn's allegations.

The government has defended its policy and on Wednesday filed a criminal complaint against Thanathorn for his criticism, accusing him of royal insult under Article 112 of the criminal code that is punishable by up to 15 years in prison.

"The deals were not negotiated independently of each other. There was no selection process or comparison so questions must be raised," Thanathorn told a news conference, during which he said the prime minister was using Article 112 to silence him.

A government spokeswoman, Ratchada Dhanadirek, has denied the prosecution was politically motivated.

Thanathorn was banned from politics for 10 years after a court dissolved his Future Forward Party last year for illegal loans.

The party won significant support among younger voters in a 2019 general election, coming third, with a campaign that focused on opposition to military influence over politics.

The government said the election was free and fair but opposition parties say it was designed to ensure former military government leader Prayut remained in power.