As speculation grows that the US could be involved in Israeli attacks against Iran, with U.S. government officials telling Bloomberg news agency that preparations are being made to launch bombing raids on Iran in the coming days, Washington has redirected military assets to the Middle East.

There are about 40,000 U.S. troops in the region right now, a U.S. official said earlier this month.

At least 30 US military aircraft have moved from bases in America to Europe in recent days. The planes are all U.S. army tanker aircraft used to refuel fighter jets and bombers.

The aircraft carrier USS Nimitz sails to the Middle East from the South China Sea, along with several guided-missile destroyers. Other warships are in the Gulf of Oman and the Persian Gulf and have already helped Israel shoot down Iranian missiles.

Washington has also moved F-16, F-22 and F-35 fighter jets to bases in the Middle East, according to Reuters news agency.

Tehran is believed to have two main underground enrichment facilities. Natanz has already been hit by Israel and Fordo is buried deep inside a mountainous complex near the city of Kom.

To penetrate the facility, the US will likely have to use GBU-57A/B Massive Ordnance Penetrator (MOP) munitions. MOPs are huge 30,000-pound (13,600-kilogram) bombs, also known as “bunker busters.”

The bomb is the only weapon of its kind thought to be capable of penetrating concrete up to 60 meters deep. Only the B-2 stealth bomber can carry the ammunition.

Recently, the US has deployed a squadron of B-2 bombers to its base on Diego Garcia Island. While the island is about 2,400 miles from Iran’s southern coast, its location on Diego Garcia would put them near Iran.

Satellite images first showed B-2 bombers deployed to Diego Garcia in late March, but more recent photos from the island no longer show the bombers there.