April 25 (Reuters) - A cargo ship contracted by the U.S. military fired on an Iranian vessel in Gulf waters on Friday, raising tension between Washington and Tehran in a region vital to world oil shipments.

In January, the United States said Iranian boats aggressively approached three U.S. navy battle ships, warning them they would explode in minutes. Iran has said it was a routine contact.

In late March, warning shots also fired by a U.S. Military Sealift Command ship against a small boat, this time close to the Suez Canal, killed an Egyptian civilian.

Any military action in the Strait of Hormuz in the Gulf would knock out oil exports from OPEC's biggest producers, cut off the oil supply to Japan and South Korea and knock the booming economies of Gulf states.

Here are some key facts on what passes through the international waterway and some of the direct economic consequences of any attack on merchant shipping.

-- 2.9 billion deadweight tonnes passes through the strait every year.

-- Crude oil exported through the Strait rose to 750 million tonnes in 2006.

-- 27 percent of transits carry crude on oil tankers, rising to 50 percent if petroleum products, natural gas and Liquefied Petroleum Gas transits are included.

-- Transits for dry commodities like grains, iron ore and cement account for 22 percent of transits.

-- Container trade accounts for 20 percent of transits, carrying finished goods to Gulf countries.

Oil exports passing through Hormuz:

(2006 figures)

Saudi Arabia -- 88 percent

Iran -- 90 percent

Iraq -- 98 percent

UAE -- 99 percent

Kuwait -- 100 percent

Qatar -- 100 percent

Top 10 importers of crude oil through Hormuz

(2006 figures)

Japan -- Takes 26 percent of crude oil moving through the strait (shipments meet 85 percent of country's oil needs)

Republic of Korea -- 14 percent (meets 72 percent of oil

needs)

United States -- 14 percent (meets 18 percent of oil needs)

India -- 12 percent (meets 65 percent of oil needs)

Egypt -- 8 percent (N.B. most transhipped to other

countries)

China -- 8 percent (meets 34 percent of oil needs)

Singapore -- 7 percent

Taiwan -- 5 percent Thailand -- 3 percent

Netherlands -- 3 percent (Source: Lloyd's Marine Intelligence Unit) (Reporting by Stefano Ambrogi; editing by James Jukwey)

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