During his state visit to Britain, U.S. President Donald Trump said that Washington and London are "determined to ensure" Iran does not develop nuclear weapons and stops supporting terrorism.
"Among the pressing threats facing our nations is the development and spread of nuclear weapons -- perhaps that's our biggest threat," Trump told a joint press with British Prime Minister Theresa May on June 4 following a meeting at her Downing Street residence.
"The United States and United Kingdom are determined to ensure that Iran never develops nuclear weapons and stops supporting and engaging in terrorism," he said, adding: "And I believe that will happen."
Trump's comments come amid heightened tensions between Iran and the United States and its allies in the Persian Gulf.
Washington a year ago withdrew from a 2015 nuclear accord between world powers and Iran that curbed the country's nuclear program in exchange for relief from crippling economic sanctions.
In announcing the U.S. pullout, Trump said the terms were not tough enough to prevent Iran from developing nuclear weapons and did not address the country's missile program or its support for militants in the region.
Since then, Washington has reimposed sanctions, stepped up its rhetoric, and beefed up its military presence in the Middle East, citing "imminent threats" from Iran.
Tehran has dismissed these allegations.
It also denies supporting insurgent activity and says its nuclear program has been strictly for civilian energy purposes.
On NATO, Trump said he and May had agreed that "our NATO allies must increase their defense spending."
"We expect a growing number of nations to meet the minimum 2 percent of GDP requirement. To address today's challenges, all members of the alliance must fulfill their obligations. They have no choice," he said.
Trump has repeatedly criticized NATO's European members for not spending enough on their armed forces.