Image credit: Hassan Ammar/AP Photo

In hopes of protecting the Strait of Hormuz - its key oil-shipping route - the United States has been quietly building up forces in the Persian Gulf to discourage Iran from following through on threats to shut down the waterway.

In light of July 1 sanctions by the United States and Europe making it harder for Iran to export oil to Europe, Iranian lawmakers have reportedly demanded the strait to be shut down.

The Strait of Hormuz connects the Persian Gulf to the Arabian Sea and an estimated one-fifth of the world's oil travels through it.

The U.S. military has bases all over the Persian Gulf region and has kept about 40,000 troops in the region. They're there to reassure American allies in the region worried about potential Iranian military threats.

So far, the United States has sent additional fighter jets and beefed up its naval presence. The USS Ponce has just arrived in the waters off of Bahrain, with mine sweeping helicopters on board.

The Ponce is an old amphibious ship that has been converted into an interim Afloat Forward Stationed Base, a new kind of vessel staffed by a mixed crew of civilian and Navy sailors that can remain in the Gulf and serve as a floating base for minesweepers and helicopters operating in the Gulf region. The ship could also be used as a mobile staging base for special operations forces if the need arose.

Four additional minesweepers also arrived in the Gulf two weeks ago, doubling the number of such ships there, a Navy official told ABC News. The official said thet are "wholly defensive in nature and are used to keep sea lanes clear so that commercial shipping may safely occur in international waters."

A major minesweeping exercise in the Gulf is planned for September, with 19 countries participating.

The Navy maintains a two-carrier presence in the Middle East, and for for much of this year has kept up a rotation that keeps an aircraft carrier in the Persian Gulf. The carriers operate in the Gulf for two- to three-week stretches and then transit out of the Strait of Hormuz. Usually within a few days the other carrier moves into the Gulf for its turn.

Just last week the carrier USS Abraham Lincoln transited out of the Strait of Hormuz after spending two and a half weeks in the Gulf. When not in the Gulf, the other carrier operates out of the Arabian Sea flying aircraft over Afghanistan.

The Air Force acknowledged in April that it had sent a complement of F-22 fighters to "Southwest Asia," but did not specifically said that they were operating out of Al Dhafra in the United Arab Emirates.

A Defense official confirms that additional F-15E fighters have also been sent to the region, but did not identify the country they'd been sent to.

The Army has about 12,000 soldiers in Kuwait. A combat brigade that pulled out of Iraq in December with the rest of U.S. forces remained in Kuwait until June. A few weeks ago that brigade from the 1 st Cavalry Division was replaced by another brigade from the 3 rd Infantry Division. In addition to that, the Army has other National Guard combat brigades as well as a combat aviation brigade in Kuwait.

Iran's Revolutionary Guard launched a barrage of missiles today at "mock enemy bases" as part of a major war games exercise aimed at dissuading any potential outsider attack.

The mock enemy bases were located in desert areas, which is where U.S. forces are located in Kuwait. America's Fifth Fleet is in Bahrain.

Reports from Iran's Islamic Republic News Agency alluded to diplomatic conflict between the United States and Iran.

ABC News' Luis Martinez and Lee Ferran contributed to this story.