A failed attack on a container ship transiting the Suez Canal has raised concerns that as Egypt descends into widening violence the strategic waterway, could become a target for Islamist militants.

The blockage or closure of the 120-mile canal, the world's second most important maritime choke point for oil and liquefied natural gas bound for Europe and the United States, would have a potentially significant impact on global trade.

The narrow waterway that links the Mediterranean and Red Seas could also become a target for terrorists specifically seeking to disrupt energy supplies since some 800,000 barrels of northbound crude oil from the Persian Gulf and 1.4 million barrels of refined petroleum products pass through the canal daily, according to the U.S. Energy Information Administration.

On top of that, an additional 1.7 million barrels of crude is pumped through the 200-mile Sumed pipeline that runs parallel to the canal from Port Suez at its southern end to terminals on the Mediterranean coast, for cargoes too big to transit by ship.

The Aug. 31 attack on the Panamanian-flagged, Chinese-owned Cosco Asia with rocket-propelled grenades was the first confirmed assault on shipping in the turmoil triggered by the July 3 ouster of Islamist President Mohamed Morsi by the military.

That was a development the U.S. private intelligence consultancy Stratfor warned "will bear careful watching due to its possible impact on global trade."

But analyst Scott Stewart stressed that "while the canal is long and difficult to totally secure, it would be very difficult to conduct an attack that would block the canal."

Even so, the waterway's eastern bank lies in the Sinai Peninsula, where the Egyptian army is currently engaged in a major operation against jihadist groups based in the vast region of desert and mountains.

That makes it vulnerable to attack by militants heavily armed with weapons smuggled from Libya and committed to avenging Morsi's ouster.

The canal is also vital to the U.S. military for the transit of the navy's aircraft carriers and other warships deploying in the Red Sea and Arabian Sea for operations against Afghanistan and to counter Iran in the oil-rich Persian Gulf. Some 35-45 ships of the 5th Fleet pass through the canal annually.

Kataeb al-Forqan, one of the Islamist groups in Sinai, claimed responsibility for the Aug. 31 attack in the northern sector of the canal and released a 52-second video showing two men firing rocket-propelled grenades at the Cosco Asia, which Cairo said was not damaged. Three suspects have been arrested.

The group said in a Sept. 2 communique it carried out the attack because the canal "has become a safe passageway for the Crusader aircraft carriers to strike the Muslims and it is the artery of the commerce of the nations of unbelievers and tyranny."

It warned: "We can target the international water passage morning and night, along its entire length ... and we will return to target it whenever we wish."

The Egyptian military has stepped up security along the whole waterway, which is a vital economic asset for the Arab world's most populous state and generates around $5 billion a year, the country's third biggest foreign currency earner excluding exports.

That makes it an even more important target for militants.

The waterway, built in 1859-69 by the French engineer Ferdinand de Lesseps, has been closed down before.

During the 1956 British-French-Israeli attack on Egypt, the Egyptian military scuttled 40 ships which shut it for about six months.

Although vessels in the canal, only about 900 feet wide, are highly vulnerable to fire from a variety of weapons systems from the two banks, it's difficult to sink a ship like the Cosco Asia, which is about the same size as the USS Ronald Reagan, a nuclear-powered carrier.

Al-Qaida suicide attacks on the USS Cole in October 2000 and the French tanker Limberg in March 2002, both off Yemen, using small boats packed with hundreds of pounds of high explosives failed to sink those ships.

But scuttling large vessels in the canal remains a major concern.

The canal was also closed for eight years after the 1967 Middle East war when Israel defeated Egypt and occupied Sinai up to the eastern bank of the canal for nearly a decade, forcing tankers to take the long route around Africa.