Iran on Monday claimed responsibility over security in the Persian Gulf, with its Foreign Minister Javad Zarif warning that the country will no longer overlook violations. Zarif’s remarks, coming one day after Iran stated it had seized a third oil tanker in the Persian Gulf last week, indicate that Iran may be ready to take more action against vessels that want to pass the Strait of Hormuz between Iran and the United Arab Emirates.

Iran had already claimed to have seized two oil tankers in July. It said the third vessel belonged to Iraq, but Iraq denied this. In early July, the UK captured an Iranian tanker near Gibraltar.

Tensions between Iran and the US and its allies have escalated in the past few months. Tehran recently started violating the 2015 Iran nuclear deal, which was abandoned by the Trump administration last year. Last week, the US imposed sanctions on Zarif, with US Treasury Secretary Steven Mnuchin stating that Zarif “implements the reckless agenda of Iran’s Supreme Leader.” Iran dismissed those sanctions as “childish.”

Read more: Iran Signals More Escalation With Warning on Gulf Violations