U.S. President Donald Trump repeatedly asked his national security team during his first year in office to draw up a plan to blow up Iranian "fast boats," Axios reported on Monday. Trump reportedly asked then Defense Secretary James Mattis, referring to Iranian boats in the Persian Gulf, "Why don't we sink them?"

Axios quoted two sources who say they directly heard Trump's requests and three other former senior officials reportedly briefed on them. "So these boats, they get in, they come in really fast, they come in really close… and they might have explosives on them and we don't even know," Trump reportedly told staff. "Can you believe this? And we don't do anything?"

However, the sources told Axios such "disproportionate" response at a time when Iranian vessels were harassing the U.S. Navy less than previous years could have quickly led to war. Mattis, who later resigned in protest of Trump's Syria policy, reportedly never provided such a plan.

The report adds that when trump asked then National Security Adviser H.R. McMaster about it during a daily brief, the latter replied: "Mr. President, this has happened in the past, but DOD (Department of Defense) is telling us it hasn't happened lately… so they're not that concerned about it."

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Iran's Revolutionary Guards said in early January they plan to upgrade their speed boats in the Gulf with radar-evading stealth technology and new missile launchers, as tensions rise between Tehran and Washington in the vital oil shipping route.

Ending a long absence of U.S. aircraft carriers in the region, the USS John C. Stennis entered the Gulf in late December, and was shadowed by the Revolutionary Guards' speed boats.

Open gallery view File photo: U.S. President Donald Trump with Defense Secretary James Mattis in the Cabinet Room at the White House in Washington, October 23, 2018. Credit: Leah Millis/Reuters

There have been periodic confrontations between the Revolutionary Guards vessels and U.S. military in the Gulf, although the number of incidents has dropped in recent months.

The Revolutionary Guards launched in late December war games in the Gulf, where third of the world’s sea-borne oil passes through, and warned that its forces were ready to respond to any hostile U.S. action.

In an indirect threat to Saudi Arabia and other U.S. allies in the region, the head of the Iranian armed forces warned that any Iranian confrontation with U.S. forces might also target Gulf nations that he said had invited them into the region.

The Wall Street Journal reported on Sunday that National Security Adviser John Bolton requested the Pentagon to provide Washington with military options to strike Iran, after three mortars launched by Iran-affiliated militants fell near the U.S. Embassy in Baghdad.

The incident occurred in early September. No one was wounded, as the shells fell in an open lot, but the event apparently spurred Washington to discuss the possibility of a military response.

It is unclear whether President Trump knew of Bolton's request or if concrete plans were drawn out for a strike, but according to the official, the Pentagon agreed to develop a set of options to attack Iran.

A U.S.-Iranian war of words has escalated since Trump took Washington out of a world powers’ nuclear deal with Iran in May, and reimposed sanctions on its banking and energy sectors.

Iran has warned that if it cannot sell its oil due to U.S. pressure, then no other regional country will be allowed to do so either, threatening to block the Strait of Hormuz in the Gulf.

The Guards’ naval arm lacks a strong conventional fleet. However, it has many speed boats and portable anti-ship missile launchers, and can lay mines.