The Trump administration is urging Europe to impose tough new sanctions on Iran over its ballistic missile programme.
The call comes as Secretary of State Mike Pompeo is to meet European officials in Brussels this week and after the US and others condemned an Iranian missile launch over the weekend.
Iran was also a topic of conversation when Mr Pompeo met Israeli Prime Minister Benjamin Netanyahu in Brussels on Monday night.
Mr Pompeo plans to talk about Iran when he meets his counterparts from Britain, France and Germany on Tuesday while he is in Belgium for a meeting of Nato counterparts.
US special envoy for Iran Brian Hook rejected Iran's insistence that its missile programme is defensive.
He told reporters traveling with Mr Pompeo that Iran's continued missile development and testing is a threat to the region and beyond and in defiance of UN Security Council demands.
Mr Hook said US discussions with the Europeans about missile sanctions are gaining traction. Those talks center on slapping penalties on companies and people involved in Iran's program.
"It is a grave and escalating threat, and nations around the world, not just Europe, need to do everything they can to be targeting Iran's missile program," Mr Hook said.
Mr Hook's comments on Monday were the latest salvo in an escalating US campaign against Iran since President Donald Trump pulled out of the 2015 nuclear deal in May.
"Iran is on the wrong track, and our campaign of maximum economic pressure is designed to starve the regime of revenue it needs," he said.
On Thursday, Mr Hook accused Iran of violating a UN ban on Iranian arms exports by sending weapons to its proxies in Afghanistan, Iraq, Lebanon, Syria and Yemen.
On Saturday, Mr Pompeo denounced Iran for test-firing a medium-range ballistic missile capable of carrying multiple warheads that could reach parts of Europe.
"We are accumulating risk of escalation in the region if we fail to restore deterrence," he said.