The US says it wants to create an international military coalition to safeguard waters around Iran and Yemen.
Marine General Joseph Dunford, chairman of the US Joint Chiefs of Staff, said he wanted to "ensure freedom of navigation" in the region, which provides essential trade routes.
The US has blamed Iran for attacks on oil tankers in May and June.
Gen Dunford said the US was talking to a number of countries with the "political will" to support the plans.
The US would provide "command and control" ships, leading surveillance efforts, he said.
However, the aim would be for other countries to offer boats to establish patrols nearby, and escort commercial ships carrying their flags through the area.
Gen Dunford said the US would "work directly with the militaries to identify the specific capabilities" each country has to support the initiative.
The Straits of Hormuz and Bab al-Mandab are essential strategic marine locations, providing access from the ocean into the Gulf and the Red Sea.
He said the size of the initiative depended on the number of countries that decided to take part.
"With a small number of contributors, we can have a small mission," he said.
"We'll expand that as the number of nations that are willing to participate identify themselves."
Everyday, nearly four million barrels of oil pass through Bab-al Mandab to the rest of the world.
Last month the US blamed Iran for attacks on two tankers in the Gulf of Oman - accusations denied by Iran. It followed an attack on four tankers in the region in May.
Days after the June attacks, an unmanned US drone was shot down by Iranian forces in the Gulf.
Iran said it had violated Iranian airspace and would send a "clear message to America". The US insisted the drone had been over international waters. President Donald Trump tweeted: "Iran made a very big mistake!"
The US planned for retaliatory air strikes, which were later cancelled.
Iran has said it would close the Strait of Hormuz if, as President Trump hopes, it becomes unable to export oil due to sanctions the US imposed since pulling out of the Iran nuclear deal.
However, speaking to the BBC, Iran's ambassador to the UN remained defiant.
"We have managed under different situations worse than we have today, and I am sure we can manage again," Majid Takht-Ravanchi said.
He also accused Europe of failing to honour their commitments under the 2015 deal.