As part of its war on Iran, the United States has tightened sanctions against Tehran's government and the IRGC in an attempt to economically stifle them.

The United States on Monday issued sanctions against 12 individuals and entities that it said facilitated the sale and shipment of Iranian oil to China, days ahead of US President Donald Trump's visit to Beijing.

In a statement, the US Treasury alleged that Iran's Islamic Revolutionary Guard Corps (IRGC) "relies on front companies in permissive economic jurisdictions to obfuscate its role in oil sales and funnel the revenue to the Iranian regime." 

It listed three Iran-based individuals and nine companies -- based in Hong Kong and the United Arab Emirates -- as being subject to the new sanctions.

Sanctioned entities will see any US-based assets blocked, with all transactions with them by US entities and individuals also banned.

As part of its war on Iran, the United States has tightened sanctions against Tehran's government and the IRGC in an attempt to economically stifle them.

"As Iran's military desperately tries to regroup, Economic Fury will continue to deprive the regime of funding for its weapons programs, terrorist proxies, and nuclear ambitions," US Treasury Secretary Scott Bessent said, referring to the economic measures the US is imposing on Iran alongside its military pressure.

The war has roiled global energy markets, with Tehran having virtually blocked the key Strait of Hormuz, through which nearly a fifth of the world's oil and gas normally flows. 

Washington eased some sanctions on Iranian oil in March in an attempt to address global supply shortages, but it has since tightened restrictions again. 

Much of Iran's oil is bound for Asia, with China a major importer. Beijing is one of Tehran's biggest trading partners overall.

US President Trump is due in Beijing later this week for key talks with Chinese President Xi Jinping, with a full slate of trade disputes on the agenda.

The US-Israeli war on Iran will also top the agenda, with Washington seeking greater pressure on Tehran from Beijing.

The US State Department sanctioned three China-based satellite firms on Friday for enabling Iran's military operations.

The US Treasury Department earlier sanctioned several mainland China- and Hong Kong-based firms for aiding Iran's weapons supply.