Oil prices are moving higher as global tensions with Iran continue to escalate, sparking concerns about supply.

CNN reported that futures of Brent crude, the global benchmark, rose more than 2% Monday to reach $64.02 per barrel. U.S. oil prices saw similar gains and hit $56.83.

The gains follow news that Iran seized a British tanker in the Strait of Hormuz.

Britain has warned that it will take “robust” action if Iran does not release the ship, and the government’s emergency response committee is meeting Monday.

The episode comes after Britain detained an Iranian tanker in waters off Gibraltar. The United States and Iran are also engaged in a tense standoff. The United States last week claimed to have downed an Iranian drone, almost exactly one month after Iran shot down a US drone.

Oil has been volatile in recent months as investors try to read conflicting signals on prices. Brent crude topped $74.50 in April before falling to below $60 in June.

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