FACTBOX: How big is Iran's military?

(Reuters) - U.S., Iranian and Western diplomats have played down worries about a looming Israeli military attack on Iran's nuclear facilities, after reports of heightened tensions rattled nerves and helped drive oil prices near record highs.

Iran insists its nuclear plans are peaceful but says its forces are ready to respond to any military attack.

Following are some details about Iran's military capability. The totals include equipment held by the Revolutionary Guards, which operate on land, at sea and in the air:

* ARMED FORCES:

Iran has 545,000 personnel in active service. Major General Ataollah Salehi is the armed forces chief.

* ARMY: The army comprises 350,000 men, including 220,000 conscripts. The Islamic Revolutionary Guards Corps, viewed as the most loyal guardian of the ruling system, has another 125,000 men. In 2004 the army was organized in four corps, with four armored divisions and six infantry divisions.

-- There are nearly 1,700 tanks including some 100 Zulfiqar locally produced main battle tanks. A large number of Iran's tanks are elderly British-made Chieftains and U.S.-made M-60s.

-- Soviet-made T-54 and T-55s, T-59s, T-62s, and T-72s were also part of the inventory, all captured from the Iraqis or acquired from North Korea and China.

-- The latest Military Balance report from the International Institute for Strategic Studies says that some of the tanks' serviceability may be in doubt.

-- There are around 640 armored personnel carriers. There are 8,196 artillery pieces of which 2,010 are towed, and over 310 are self-propelled.

* MISSILES:

-- In a 2007 parade to mark the anniversary of 1980-88 Iran-Iraq war, Iran showed its Shahab-3 missile, saying it could travel 2,000 km (1,250 miles) -- enabling it to hit Israel and U.S. bases in the region. Another missile at the parade, the Ghadr-1, can reach targets 1,800 km (1,125 miles) away. It was believed to be the first time it has been shown publicly.

* NAVY: There are 18,000 naval personnel. The navy has its headquarters at Bandar-e Abbas. Iran's navy has three Russian Kilo class submarines, three frigates and two corvettes.

-- As of 2001 the regular Iranian navy was in a state of overall obsolescence, and in poor shape because they had not been equipped with modern ships and weapons. The readiness of the three frigates is doubtful, and the two nearly 40-year-old corvettes do not have sophisticated weapons.

-- In late 2007 Iran launched a new locally made submarine and a navy frigate named as Jamaran. Jane's Defence Weekly reported last November that Iran was also building missile-launching frigates copied from 275-tonne Kaman fast attack missile craft originally purchased from France in the late 1970s.

* AIR FORCE: