Iran’s supreme leader said Friday that he had banned the import of U.S. and British-made coronavirus vaccines, a surprise move that contradicts his own government’s recent efforts to ensure the country’s access to safe and effective immunizations.

Ayatollah Ali Khamenei, Iran’s highest political and religious authority, made the announcement in a televised address, calling the vaccines “forbidden.”

“They are completely untrustworthy,” he said. “If they were able to create a vaccine … why do they want to give it to us? Why don’t they use it themselves?”

He posted a tweet questioning the trustworthiness of the vaccines, which Twitter removed.

Khamenei singled out the vaccine developed in a joint venture between the U.S. pharmaceutical giant, Pfizer, and Germany’s BioNTech. He said that he had already informed the relevant authorities of his decision but was now making it public.

Data has shown that the Pfizer vaccine’s two doses — given roughly three weeks apart — are 95 percent effective. In Britain, Oxford University also joined AstraZeneca in Cambridge to develop a separate jab, which is more than 60 percent effective. Both vaccines are already in use in Britain and other countries.

The decision comes as Iran continues to struggle to bring the coronavirus under control. The country was an early hot spot — recording its first case in mid-February — and has fought ever since to bring down infection levels while grappling with the effects of U.S. sanctions.

Authorities have been reluctant to impose stringent lockdowns that would hurt the economy, while some religious clerics initially urged people to seek alternative treatments for the virus. Khamenei himself cited an unfounded conspiracy theory in March, claiming that the virus was manufactured in the United States.

On Friday, Khamenei suggested that the United States and Britain could use vaccines to “contaminate” Iran.

More than 1.2 million Iranians have been infected by the virus, according to official data, and of those, about 56,000 people have died.

The decision to ban the two vaccines will complicate the recent push by Iranian health and banking officials to ensure Iran’s access to global coronavirus treatments, including vaccines. The officials have said that U.S. restrictions on Iran’s banking and financial sectors have hindered the government’s ability to pay for medicine and other medical supplies, despite a broad exemption by the U.S. Treasury Department for humanitarian imports.

Iran’s Central Bank governor said last month that his institution was having trouble converting Iranian assets to U.S. dollars to fund Tehran’s contributions to the COVAX initiative sponsored by the World Health Organization. The project aims to secure the equal distribution of coronavirus vaccines around the globe.

U.S. sanctions call for penalties against banks who engage in prohibited transactions with Iran. The restrictions are part of the Trump administration’s “maximum pressure campaign” against Tehran.

Later, the governor, Abdolnasser Hemmati, told Iranian state television that he had received approval to transfer a $244 million payment through an unnamed bank in a “third country” for 17 million vaccine doses from COVAX, the Associated Press reported. State media has also reported that Iran will eventually receive one million vaccine doses from China.

Also in December, the director of Iran’s Red Crescent said that a group of unnamed U.S. philanthropists had arranged for the distribution of 150,000 doses of the Pfizer vaccine in Iran. On Friday, following Khamenei’s announcement, the Tasnim news agency quoted a spokesman for the Red Crescent as saying that the doses would no longer be imported.

Iran says that it has developed its own vaccine against the coronavirus and that it will soon begin Phase 1 clinical trials, in which 56 volunteers will be inoculated. Only seven people have received the vaccine so far, state media reported. It was unclear what type of technology it employs.

In the fall, Iran and Russia said they were discussing the possibility of joint production of a coronavirus vaccine, but no such effort has been announced.