The Strait of Hormuz has been relatively "quiet" in the past two months without major confrontations between American and Iranian warships, the US Navy's chief said Wednesday.

The USS Abraham Lincoln aircraft carrier passed through the Strait on Wednesday without incident, one of two carriers deployed to the region, Admiral Jonathan Greenert told a news conference.

"Things have been -- relatively speaking -- quiet in that regard," he said, adding that Iranian naval forces "have been professional and courteous, committing to the rules of the road."

The Lincoln, and another carrier, the USS Enterprise, will remain in the region part of what the Pentagon calls a routine naval presence.

The Iranian Revolutionary Guard previously had operated "too close" at times, he said.

"But frankly, that hasn't happened recently. And when I say 'recently,' I'd say in the last couple of months," the admiral said.

Iran's military drills appeared to be "in accordance with their routine," he said.

Tensions spiked in December and January as Iran threatened to close the narrow strait -- through which about one-fifth of the world's traded oil passes -- if Western countries boycotted Iranian oil exports.

Speed boats from Iran's Revolutionary Guards also approached dangerously close to US naval ships.

Since December, the US Navy has moved to bolster its presence in the Gulf.

Four mine sweeper ships are due to arrive in the area Saturday, joining four other mine sweeping vessels already in the region, according to the Fifth Fleet.

The Navy also has MH-53 Sea Stallion helicopters stationed in Bahrain, home to the Fifth Fleet headquarters.

The USS Ponce, an old amphibious warship that has been converted into a "floating base," departed Norfolk, Virginia on June 1 and is scheduled to arrive in the Gulf at the end of June or the beginning of July, the Fifth Fleet said.

The ship is supposed to support counter-mine operations and coastal patrols.