US President Donald Trump on Monday said he had imposed a 25% tariff on goods from countries with commercial ties to Iran, a move that could put pressure on Tehran as anti-government protests enter a third week.

Trump said on social media that the tariff was "effective immediately", without offering details of what constituted "doing business" with Iran.

China is Iran's largest trading partners, followed by Iraq, the United Arab Emirates, Turkey and India.

The new tariff comes after Trump threatened to intervene militarily if Tehran killed protesters. White House spokeswoman Karoline Leavitt said on Monday that military options, including air strikes, were still "on the table".

"Any Country doing business with the Islamic Republic of Iran will pay a Tariff of 25% on any and all business being done with the United States of America," Trump wrote on Truth Social on Monday.

"This Order is final and conclusive," he added.

The White House did not share additional information about the tariffs, including which countries' imports will be hit hardest.

Anger over the plummeting value of the Iranian currency, the rial, sparked protests in late December, which have grown into a crisis of legitimacy for Iran's Supreme Leader, Ayatollah Ali Khamenei.

The US-based Human Rights Activist News Agency (HRANA) says it has verified the deaths of nearly 500 protesters and 48 security personnel in Iran, while sources tell the BBC the death toll could be much higher. Thousands more have reportedly been arrested.

However, an internet blackout since Thursday evening has made it difficult to obtain and verify information. The BBC and most other international news organisations are unable to report from inside Iran.

Trump has threatened to intervene, and said on Sunday that Iranian officials had called him "to negotiate" - but added "we may have to act before a meeting".

International sanctions over Iran's nuclear programme have had a severe impact on the country's economy, which has also been weakened by government mismanagement and corruption.

On 28 December, shopkeepers took to the streets of Tehran to express their anger at another sharp fall in the rial's value against the US dollar on the open market.

Iran's currency has sunk to a record low over the past year while inflation has soared to more than 40%, resulting in sharp price rises for everyday items like cooking oil and meat.