On Sunday, Iran cut off the small amount of oil it supplies to British and French companies. It was a pre-emptive retaliation against the European Union's planned embargo of Iranian oil starting in July that is aimed at halting Tehran's nuclear development program. The U.S. and EU nations say Iran's nuclear program is aimed at producing nuclear weaponry, a claim Iran rejects.

　　On Monday, Iran threatened to extend the oil cutoff to other European countries, which together buy about 600,000 barrels of Iranian oil a day of the 2.5 million Iran exports. About two-thirds of Iran's exported oil is sent to Asian countries.

　　As the uncertainty grew, the price of crude on the New York market increased about 2 percent to more than $105 a barrel, its highest point since early last May. The price is up more than 6 percent since start of the year.

　　The price for Brent crude on the London market rose 1.3 percent Monday to more than $121 a barrel.

　　Oil financial analysts say Iran's heightened tensions with the West, along with continued economic growth in the U.S. and China, the world's two largest economies, are likely to keep oil prices high. The higher price of crude oil has already boosted gasoline prices that motorists pay in the U.S.