NEW YORK (CNN/Money) - The U.S. Navy warned Tuesday of possible attacks on oil tankers in the Middle East Gulf region by al Qaeda, sending the price of oil rising.

"According to unconfirmed reports circulating within the regional shipping community, the al Qaeda terrorist group has planned attacks against oil tankers transiting the Arabian Gulf and Horn of Africa areas," read the warning from the Navy's Maritime Liaison Office in Bahrain.

The price of October futures for a barrel of Brent oil rose 53 cents to a one-year high of $29.02 a barrel in London trading after the warning, before retreating slightly to $28.80 a barrel. In New York trading, light crude for October delivery rose as much as 47 cents to $30.20 a barrel before retreating to $29.93.

The warning came as the U.S. Homeland Security office raised the overall terrorism state of alert to "orange," the second-highest risk assessment behind a red alert. Attorney General John Ashcroft said potential targets could include the transportation and energy sectors and facilities that are recognized symbols of the United States.

Despite the warning, oil tankers are loading as normal in the Gulf, industry sources said Tuesday.

About a quarter of the world's traded oil -- or some 12 million barrels per day -- is shipped out of the strategic waters of the Gulf through the straits of Hormuz between Iran and Oman.

"It's business as usual," a senior shipping executive in the region, who received the notification, told Reuters. "An attack is only a remote possibility."

Sources said oil continued to load normally from Saudi Arabia's main terminal at Ras Tanura on the Gulf that handles well over four million barrels per day.

"There is no activity at the port to indicate any increased security and loadings are as usual," a shipping source told Reuters.

A spokesman for the U.S. Navy in Bahrain said it was the first time the Navy has released such a notice after the Sept. 11 attacks on the United States last year.

"While the U.S. Navy has no specific details on the timing or means of the planned attacks, and there are no indications that an attack is imminent, the threat should be regarded seriously," the Navy said.

"Shipmasters should exercise extreme caution when transiting strategic chokepoints such as the Strait of Hormuz or Bab-el-Mandeb, or sailing in traditional high-threat areas such as along the Horn of Africa and other confined waters," the Navy statement said.  

-- from staff and wire reports