US Secretary of State Mike Pompeo blamed Iran on Sunday for last week's attacks on oil tankers and vowed that the United States will guarantee free passage through the vital Strait of Hormuz.

Pompeo would not be drawn on what options the US is considering to protect shipping — or to punish Iran — in the wake of Thursday's attacks on two tankers in the Gulf of Oman.

“What you should assume is we are going to guarantee freedom of navigation throughout the strait,” he said in an interview on “Fox News Sunday.”

A third of the world's seaborne oil supply passes through the Strait of Hormuz, a narrow channel bordered to the north by Iran that links the Gulf with the Gulf of Oman.

“This is an international challenge, important to the entire globe. The United States is going to make sure that we take all the actions necessary, diplomatic and otherwise, that achieve that outcome,” Pompeo said.

He would not lay out US evidence for Iran's involvement in the Gulf of Oman explosions, but insisted: “It's unmistakable what happened here.

“These were attacks by the Islamic Republic of Iran on commercial shipping, on the freedom of navigation, with the clear intent to deny transit through the strait.