The US aircraft carrier Abraham Lincoln has sailed through the Strait of Hormuz, close to the coast of Iran, for the second time in recent weeks.A BBC reporter on board said an Iranian patrol boat at one point passed by two miles (3.2km) from the carrier.
The carrier was accompanied by a US cruiser and destroyer.
Iranian officials recently threatened to close the channel, through which 20% of the world's oil exports pass, in a row over oil trade embargoes.
The BBC's Jonathan Beale on board the Abraham Lincoln says the US has insisted it will keep the busy shipping lane open.
At its narrowest point, the Strait of Hormuz is only 21 nautical miles (40km) wide. Earlier, the US navy said the Iranian patrol boat passed within about half a mile of the carrier, but they later corrected this to two miles.
While travelling through the narrowest part of the strait, all fighter jets on the carrier were grounded, our correspondent says, but US Navy helicopters flew above the carrier.
He says it was clearly a carefully planned operation and the crew were pleased to have come through the most difficult stage of the voyage without incident.
A French warship and UK naval vessels accompanied the aircraft carrier in a journey through the strait last month.
As well as ensuring the shipping channel remains open, the aircraft carrier will also eventually have the task of assisting operations in Afghanistan.
The EU last month banned all oil imports from Iran amid growing concern over Tehran's nuclear programme.
Both the US and EU have since lobbied countries around the world to block Iranian oil imports.
Iran says its nuclear programme is solely for power generation, but Western nations fear Tehran is trying to develop a weapons capability.