TEHRAN — Iran's parliament speaker, Mohammad Bagher Ghalibaf, warned on Friday that no state in the region would be permitted to export oil through the Strait of Hormuz if Iran were denied access to the vital waterway. He said security in the strait was a shared responsibility.

The warning came as diplomatic friction between Tehran and European powers deepened over Iran's nuclear programme and the treatment of Western diplomats. France, Britain and Germany have pressed Iran over stalled negotiations and threatened to trigger the reinstatement of United Nations sanctions under the 2015 nuclear accord's snapback mechanism.

Roughly a fifth of the world's oil supply passes through the Strait of Hormuz, and Iranian officials have repeatedly linked the waterway's security to pressure over its economy and nuclear activity. Ghalibaf's remarks followed weeks of tension after the June conflict involving Israeli and American strikes on Iranian nuclear sites.

The statement drew attention from energy markets and Gulf governments, several of which rely on Hormuz for their own exports. A spokesman for the United States Fifth Fleet, based in Bahrain, has previously said the military maintains a presence to ensure freedom of navigation in the region.

Analysts at the International Energy Agency have warned that any disruption to the strait would push crude prices sharply higher and strain global supply chains already tested by the year's geopolitical turmoil.