"Secretary Michael R. Pompeo spoke with UK Foreign Secretary Dominic Raab today to discuss key global priorities, including countering Iran's attempts to expand its nuclear program," said State Department spokeswoman Morgan Ortagus.

She did not mention whether the conversation touched on increased tensions with Tehran over Iran's detention of a British-flagged tanker on July 19 in the Strait of Hormuz.

The seizure has been seen as a tit-for-tat move after British authorities detained an Iranian tanker off Gibraltar earlier this month on suspicion it was shipping oil to Syria in breach of EU sanctions.

Although Trump has adopted a "maximum pressure" campaign against Iran this year, his administration has made clear the tanker is primarily London's issue.

New British Prime Minister Boris Johnson's approach to handling the crisis will be under close scrutiny. It is unclear whether Johnson, who took office Wednesday, will adopt the same hardline approach to Iran as Trump.

In May 2018, while serving as foreign secretary under former prime minister Theresa May, Johnson went to Washington to try to persuade Trump not to abandon the Iran nuclear deal.

He now hopes to seal a trade deal with the US to compensate for a no-deal Brexit.

Ortagus added that Pompeo and Raab discussed "strengthening the NATO Alliance" during their call, an organization that President Donald Trump has previously criticized.

"We value our close ties with the United Kingdom as we work together to address the world's security challenges," Pompeo tweeted.

Next week, Pompeo will attend a gathering in Thailand for the Association of Southeast Asian Nations (ASEAN), as well as meetings with officials in Australia and Micronesia.