BBC.CNN WORLD NEWS

(Reuters) - The U.S. military conducted an unmanned test flight of its hypersonic Waverider aircraft, designed to move at six times the speed of sound using technology that bridges the gap between planes and rocketships, a military official said.

A B-52 bomber launched the remotely monitored, nearly wingless experimental aircraft, officially known as the X-51A, between 10 a.m. and 11 a.m. (1700 and 1800 GMT) on Tuesday, John Haire, a spokesman for the 412th test wing at Edwards Air Force Base in California, said in a statement. Results of the brief test flight will be released on Wednesday, he said.

The plan had been to conduct the test flight over the Pacific Ocean after a staging at Edwards, said Deborah VanNierop, a spokeswoman for Boeing Co, which was involved in constructing the craft, said in a statement.

The Waverider is designed to reach speeds of Mach 6 or above, fast enough to zoom from New York to London in less than an hour. But rather than commercial air travel, the military has its eye on a more readily achievable application - using it to develop high-speed cruise missiles.

The X-51A was launched off the coast of California near Naval Air Station Point Mugu, which is northwest of Los Angeles, Haire said. It flew north over the Pacific through a range that is designed for test flights.

"The X-51 is not retrievable, in other words once you fly it, it's going to end up in the ocean," Haire said.

The aircraft is known as the Waverider because it stays airborne, in part, with lift generated by the shock waves of its own flight.

Pratt & Whitney Rocketdyne designed the X-51A's "scramject" engine, which uses the forward motion of the craft to compress air for fuel combustion, according to a description of the project from the military.

After being dropped from the B-52, a solid-rocket booster is used in the initial phase of the plane's flight to bring it up to speeds that can allow its scramjet engine to take over, by inhaling air through the craft's forward momentum.

In 2004, NASA reached a speed of Mach 9.6, or nearly 7,000 miles per hour, with a jet-powered aircraft. But that vehicle, known as X-43, only flew for a few seconds and its copper-based engine was not designed to survive the flight.

Engineers have hoped to see the hypersonic X-51A travel for five minutes of powered flight. For protection from extreme heat, it uses insulation tiles, similar to those on the NASA space shuttle orbiters, according to a 2011 military description of the project.

Hypersonic flight is normally defined as beginning at Mach 5, which is five times the speed of sound.

(Reuters) - Iran ordered a halt to its oil sales to Britain and France on Sunday in a move seen as retaliation against tightening EU sanctions, as a team of U.N. inspectors flew to Tehran to press the Islamic Republic over its disputed nuclear program.

The European Union enraged Tehran last month when it decided to impose a boycott on its oil from July 1. Iran, the world's fifth-largest oil exporter, responded by threatening to close the Strait of Hormuz, the main Gulf oil shipping lane.

On Sunday, its oil ministry went a step further, announcing Iran has now stopped selling oil to France and Britain altogether - a powerful yet largely symbolic message since neither European nation relies on Iranian crude imports.

"Exporting crude to British and French companies has been stopped ... we will sell our oil to new customers," spokesman Alireza Nikzad was quoted as saying on the ministry website.

Iran, which denies Western allegations that it is seeking to make nuclear weapons, has ramped up its rhetoric in recent weeks while also expressing willingness to resume negotiations on its nuclear program.

A five-member team from the U.N. International Atomic Energy Agency (IAEA) flew to Tehran late on Sunday for talks, although Western diplomats have played down any hopes of a major breakthrough in the two-day meeting.

"I'm still pessimistic that Iran will demonstrate the substantive cooperation necessary," one envoy said in Vienna.

Yet the outcome of this week's discussions is important and will be watched closely because it could either intensify the standoff or offer scope to reduce tensions.

The European Commission says the bloc would not be short of oil if Iran stopped crude exports as it has enough stock to meet its needs for around 120 days.

Industry sources said European oil buyers were already making big cuts in purchases from Iran months in advance of EU sanctions. France's Total has stopped buying Iranian oil while debt-ridden Greece is most exposed to Iranian crude disruption among European countries.

MILITARY STRIKE?

Iran says its nuclear program is entirely peaceful but its refusal to curb uranium enrichment, which can have both military and civilian purposes, has raised concerns.

Western powers have not ruled out using force against Iran, and there has been an intense public discussion in Israel about whether it should attack Iran to stop it making a nuclear bomb.

However, on Sunday the top U.S. military officer said a military strike would be premature as it was not clear that Tehran would use its nuclear capabilities to build an atomic bomb.

"I believe it is unclear (that Iran would assemble a bomb) and on that basis, I think it would be premature to exclusively decide that the time for a military option was upon us," said General Martin Dempsey, chairman of the U.S. military's Joint Chiefs of Staff.

He said he believed the Iranian government was a "rational actor."

The West has expressed some optimism over the prospect of new talks with Tehran, particularly after it sent a letter to EU foreign policy chief Catherine Ashton last week promising to bring "new initiatives" to the table.

"In these negotiations, we are looking for a way out of Iran's current nuclear issue so that both sides win," Iranian TV quoted Foreign Minister Ali Akbar Salehi as saying on Sunday.

Oil is a major part of Iran's export revenues and an important lifeline for its increasingly isolated economy. It has little refining capacity and has to import about 40 percent of its gasoline needs for domestic consumption.

Tightening sanctions, combined with high inflation, have squeezed the ability of working-class Iranians to feed themselves and their families, and this uncertainty forms the backdrop to a parliamentary vote on March 2.

"Everything's become so expensive in the past few weeks," said Marjan Hamidi, an Iranian shopper in Tehran, "But my husband's income stays the same. How am I going to live like this?"