Tensions between Washington and Tehran have been heightened since Trump took office, with the president unilaterally pulling out of the nuclear deal last year, reimposing sanctions and announcing additional military resources to the region to counter what officials say are threats posed by Iran and its proxies.
In the past three months, half a dozen tankers owned by a range of countries suffered damage in the Gulf of Oman.
The marine coalition plan has only been finalized in recent days and would involve the U.S. providing command ships and surveillance so that allied vessels can patrol the area and protect tankers flagged to their respective nations, Dunford said.
"We're engaging now with a number of countries to see if we can put together a coalition that would ensure freedom of navigation both in the Strait of Hormuz and the Bab al-Mandab," the general told Reuters.
The Strait of Hormuz leads into the Gulf of Oman and the Bab al-Mandab separates Yemen from the Horn of Africa. While U.S. officials have floated some sort of security operation to guard the former, the latter's inclusion in the plan appears to be a new element.
The Bab al-Mandab is also a key oil tanker route, and the U.S. and its regional allies say they are worried about attacks by Yemen's Houthi rebels, who they say are backed by Iran.
"I think probably over the next couple of weeks we'll identify which nations have the political will to support that initiative and then we'll work directly with the militaries to identify the specific capabilities that'll support that," Dunford said.
All this plays out as the disagreement over Iran's nuclear program continues to unravel.
Iran continued to comply with the deal for months even after Trump withdrew from it and reimposed sanctions last year. But in recent weeks it has ticked its level of uranium enrichment above the terms still agreed with the other signatories.
On Wednesday, Majid Takht-Ravanchi, Iran's ambassador to the United Nations, told the BBC that European nations needed to do more to compensate it for the losses inflected by U.S. sanctions.
Asked about the report, a Ministry of Defense spokesman would not comment on the incident, only telling NBC News that "the UK maintains a long standing maritime presence in the Gulf" and that it was "continuously monitoring the security situation there and are committed to maintaining freedom of navigation in accordance with international law."
Alexander Smith is a senior reporter for NBC News Digital based in London.