The United States wants to build a maritime coalition to stop attacks on tankers in waters off Iran, the top U.S. general said Tuesday.

Marine General Joseph Dunford, the chairman of the Joint Chiefs of Staff, said that over the next two weeks he hoped to enlist allies into a coalition to safeguard these waters.

Washington and some of its allies blame Tehran for a string of sabotage incidents on ships in the Gulf of Oman, a key waterway through which about a third of the world's oil tanker traffic passes.

Iran, which is locked in a wider standoff with the U.S. over the nuclear deal they both signed in 2015, denies any involvement.

Meanwhile, a top U.S. official said Wednesday that Washington is seeking an alternative to the landmark nuclear deal signed by the administration of President Barack Obama.

Iran was complying with the deal's main conditions, and its European cosignatories want to keep it alive, but President Donald Trump withdrew from it last year complaining it was too soft.

Brian Hook, the U.S. special representative for Iran, told Al-Jazeera that the U.S. is seeking a Congress-approved replacement for the agreement.

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.

The damage to Japanese oil tanker Kokuka Courageous off the port of the Gulf emirate of Fujairah on June 19, 2019. Mumen Khatib / AFP - Getty Images

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.

Meanwhile, the British Royal Marines boarded and seized an Iranian tanker last week suspected of attempting to deliver oil to Syria, in breach of E.U. sanctions.

Iran's President Hassan Rouhani said Wednesday that Britain "will realize the consequences" of seizing the ship, according to the Tasnim news agency, without specifying what he meant.

Also on Wednesday, The London Times newspaper reported that one of its frigates, HMS Montrose, was deployed to shadow a tanker flagged to the Isle of Man as it moved through the Gulf.

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."