The US secretary of state said in an interview with Fox News on Monday “the responsibility in the first instance falls to the United Kingdom”.
“This is a bad regime, it’s not honouring the people of Iran, they’ve not conducted what amounts to national piracy — a nation state taking over a ship that’s travelling in international waters — this is the kind of behaviour we’ve seen out of Iran for 40 years.
"The United States has a responsibility to do our part, but the world has a big role in this too to keep those sea lanes open,” said Mr Pompeo.
Confrontation between the United States and Iran has spiralled since last year when President Donald Trump pulled out of an international agreement signed by his predecessor Barack Obama which guaranteed Iran access to world trade in return for curbs to its nuclear programme.
Since then, Iran has stepped up its nuclear activity beyond limits in the deal and Washington has accused Tehran of attacking ships in the Gulf. In June, after Iran shot down a US drone, Trump ordered retaliatory air strikes, only to abort them minutes before impact, the closest the United States has come to bombing Iran in their 40 year history of animosity.
Last week the United States said it had shot down an Iranian drone, which Tehran denied.
Washington's major European allies Britain, France and Germany opposed Trump's decision to quit the nuclear deal and have tried to remain neutral. But Britain was drawn more directly into the confrontation on 4 July when its Royal Marines seized an Iranian tanker off Gibraltar, accused of violating European sanctions on Syria.
Iran repeatedly threatened to retaliate for that incident and has made little secret that its capture of the Stena Impero two weeks later was intended as a retaliatory move. It says the ship is being held over safety concerns and the 23-member crew, including 18 Indians and no British citizens, are safe.
On Monday, Mr Pompeo also dismissed Iran’s announcement it had captured 17 spies working for the CIA and sentenced some to death.
Iran made the announcement in state media, saying the alleged spies had been arrested in the year before March 2019. Such announcements are not unusual in Iran, but the timing has raised concerns that Tehran is hardening its position in its standoff with Western powers.
“The Iranian regime has a long history of lying ... I would take with a significant grain of salt any Iranian assertion about actions that they’ve taken,” Mr Pompeo said.
Mr Pompeo declined to comment about any specific cases, but added: “There’s a long list of Americans that we are working to get home from the Islamic Republic of Iran.”
Donald Trump also refuted the reports in a tweet on Monday morning, writing, “The Report of Iran capturing CIA spies is totally false.”
“Zero truth,” the president wrote. “Just more lies and propaganda (like their shot down drone) put out by a Religious Regime that is Badly Failing and has no idea what to do.”
“Their Economy is dead, and will get much worse,” he added. “Iran is a total mess!”
Additional reporting by Reuters