Britain's Treasury said Tuesday it had ordered the assets of five men frozen in connection with the alleged Iranian plot to assassinate Saudi Arabia's ambassador to the United States.
The finance ministry confirmed that it had acted under the Terrorist Asset Freezing Act, after ministers pledged action in response to the purported plan to kill Saudi envoy Adel Al-Jubeir in a bomb attack.
The decision does not necessarily mean that the five men hold assets in Britain.
Two men have been charged by U.S. authorities, who accused them of attempting to hire an alleged Mexican drug cartel member to carry out the killing.
U.S. officials have described the plot as a clumsy but serious operation by Iran's elite foreign action unit, the Quds Force.
A spokesman for Britain's Treasury, who spoke on condition of anonymity in line with policy, said the ministry had imposed asset freezes against five men.
They include both men charged in the case _ Manssor Arbabsiar, a 56-year-old U.S. citizen who also holds an Iranian passport, and Gholam Shakuri, an alleged member of Iran's Quds Force, who is at large in Iran.
Britain also froze the assets of three other men _ Hamed Abdollahi, a senior Quds officer alleged to have helped coordinate the plot, Abdul Reza Shahlai and Qasem Soleimani, the commander of the Quds force who allegedly oversaw the plot. The U.S. last week acted against the same five men.
British Foreign Secretary William Hague told the House of Commons last week that the alleged plan "would appear to constitute a major escalation in Iran's sponsorship of terrorism outside its borders."
He said talks were ongoing between the United States, Britain, Saudi Arabia and the European Union over whether to impose additional sanctions, which could include measures against Iran's regime, or specific entities.
"We are in close touch with the U.S. authorities and will work to agree an international response," Hague said.
U.S. President Barack Obama said last week that officials at the "highest levels" of the Iranian government must be held accountable.
Iran has strongly denied any involvement in the alleged plot.
U.S. National Security Council spokesman Tommy Vietor said he welcomed Britain's decision to impose the sanctions.
"This sends yet another message that the international community rejects this flagrant violation of international law," Vietor said in a statement.
Darlene Superville in Washington contributed to this report