Tensions between Iran and the United States are ratcheting up as the Islamic Republic finds itself increasingly backed into a corner.

Tehran Tuesday made an implicit threat to the U.S. Navy 5th Fleet in the Persian Gulf, saying it wouldn't tolerate a return to the gulf of another U.S. aircraft carrier following last month's departure of the USS John C. Stennis.

Earlier Iran test-fired two new cruise two missiles at the end of a 10-day naval exercise near the Strait of Hormuz -- a visual punctuation to Tehran's earlier threats and boasts that it had the capability to close the vital passageway for oil tankers.

"Iran will not repeat its warning ... the enemy's carrier has been moved to the Sea of Oman because of our drill," Iranian army chief Ataollah Salehi said. "I recommend and emphasize to the American carrier not to return to the Persian Gulf.

"I advise, recommend and warn them over the return of this carrier to the Persian Gulf because we are not in the habit of warning more than once."

Tehran's bombast and saber-rattling is understandable. New U.S. economic sanctions against the Tehran regime -- and those soon possible from the European Union -- over Iran's intransigence regarding its suspect nuclear program cut to the heart of the regime and the country --oil, and its dependence on it.

Petroleum accounts for about 60 percent of Iran's economy and as much as 80 percent of its foreign exchange earnings, when combined with natural gas exports. It ships abroad an estimated 2.4 million barrels of crude oil a day.

Earlier sanctions against Iran by the United States and Europe targeted individuals and companies. New U.S. sanctions, contained in a U.S. defense bill and signed by U.S. President Barak Obama, target Iran's central bank. Any financial institution that does business with Iran's central bank will be barred from doing business in the United States. Thus, financial institutions that once transferred payments to Tehran from its oil export customers have to cease doing so if they want to do business with U.S. concerns.

The European Union, meanwhile, is considering new sanctions this month, including high tariffs or even the possibility of a blockade of Iranian crude and other petroleum products to member nations.

"France ... wants sanctions toughened and the president (Nicolas Sarkozy) has made two concrete proposals on that front -- the first being the freezing of Iranian central bank assets, a tough measure," French Foreign Minister Alain Juppe said in a television interview.

At the heart of the push-and-shove match is Iran's nuclear program, which Tehran says is for power generation. Western governments suspect the program is for the development of nuclear weapons. The International Atomic Energy Agency, an arm of the United Nations, in a recent report on Iran indicates the Western powers may be correct in their assessment.

In recent weeks Iran has stepped up its aggressive pronouncements. Vice President Mohammad Reza Rahimi said no oil would pass through the Strait of Hormuz if new sanctions are imposed against Tehran.

Tehran -- with its small attack boats, submarines and missiles, does have to ability to close the waterway in the short time -- the U.S. 5th Fleet has the wherewithal to reopen it -- and cause economic disruption around the world. But Iran would also hurt itself since its own crude passes through the Strait of Hormuz to customers in Asia, such as South Korea and China.

Iran is increasingly caught between the proverbial rock and a hard place. And how it reacts is anyone's guess but it would be a mistake to assume what the West sees as a rational course of action would be viewed in the same light by Tehran.