US National Security Council spokesman John Kirby said on Friday that the United States has detected repeated Iranian threats to commercial shipping in Gulf waters, and that the Pentagon will begin to strengthen its defense position in the region.

Kirby explained that Iran harassed, attacked or interfered with the navigational rights of up to 15 merchant vessels.

Kirby added, in a press briefing, that "the Department of Defense will take a series of measures to strengthen our defense position in the Gulf." He said U.S. Central Command would provide additional details of these reinforcements in the coming days.

The U.S. military did not immediately respond to requests for comment.

This comes after Iran seized two oil tankers a week earlier this month in Gulf waters, and demanded their release, in the latest escalation of a series of detentions or attacks on commercial ships in the Gulf since 2019.

The U.S. Navy's Fifth Fleet, based in Bahrain, said on May 3 that Iran's Islamic Revolutionary Guard Corps (IRGC) navy had seized the Panamanian-flagged oil tanker Neofi as it passed through the Strait of Hormuz.

The incident came days after Iran seized a Marshall Islands-flagged oil tanker in the Gulf of Oman.

Kirby said the United States strongly condemned actions that threaten and interfere with commercial navigation and that Washington would not allow foreign powers to endanger navigation in Middle East sea lanes.

Kirby said the United States had detected repeated Iranian threats and attacks on commercial shipping companies exercising navigational rights in international waters.

About a fifth of the world's crude oil and petroleum products pass through the Strait of Hormuz, located between Iran and Oman, according to data from analytics firm Vortexa.