Britain wants to further isolate Iran's financial sector, accusing Tehran of suppressing human rights within its own borders and helping to suppress human rights in Syria.

British Foreign Secretary William Hague Thursday accused Iran of helping Syrian President Bashar al-Assad suppress anti-government protesters.

Speaking outside a meeting of European Union foreign ministers in Brussels, Hague said there is a link between Tehran's crackdown on opposition groups and Syria's violent crackdown on protesters. He said Britain is pushing for an EU agreement to intensify economic sanctions against Iran.

Britain on Wednesday expelled all Iranian diplomats from the country and shut its embassy in Tehran after it was attacked by an angry mob a day earlier.

The tense relations between Britain and Iran have been deteriorating in recent weeks. The Iranian parliament voted earlier this week to downgrade diplomatic relations with London. The vote followed Britain's decision to strengthen sanctions against Iran by cutting all links with its banks.

China on Thursday expressed concern about the potential for the situation to spiral out of control.

Chinese Foreign Ministry spokesman Hong Lei told reporters Thursday all sides needed to “remain rational, calm and restrained, and avoid emotional moves to escalate the conflict.”

Hundreds of students gathered outside the British embassy in Tehran Tuesday, chanting “Death to Britain.” Several protesters scaled the fence before ransacking the compound. Embassy staff was forced to flee through a back door.

The United States and Canada also tightened sanctions in response to Iran's pursuit of a nuclear program that U.N. experts say appears intended to build weapons. Iran says its nuclear program is peaceful.