TEL AVIV, Israel — More than 1,000 U.S. troops and some of the U.S. Army’s most sophisticated weaponry arrived in Israel this week to practice shooting down ballistic missiles to protect Israel from potential adversaries, most likely Iran.

The missile defense exercise, called Juniper Cobra, has been a biennial event since 2001. But this year’s training comes at a time of increased regional tensions, with deep concerns about Iran’s suspected plans to build a nuclear weapon.

"[The exercise] has to be viewed within the context of Iran getting closer to a nuclear weapon. It’s to provide reassurance to Israelis, and to demonstrate the depth of our concern to everybody else," said John Pike at the globalsecurity.org Web site.

"It’s a very prompt and sizable demonstration of what the new administration’s missile defense plans are."

Last month, President Barack Obama laid out plans for a missile shield against Iran, defending Europe and the Middle East. That plan would emphasize countering short- and medium-range ballistic missiles with interceptors based on ships, rather than intercontinental missiles from land-based interceptors.

The new plan illustrates a change in the perception of the threat, experts said, especially from Iran.

"The trends in the proliferation of ballistic missiles ... potentially with nuclear weapons, is creating a higher sense of urgency," said Baker Spring at the Heritage Foundation.

"Obviously Iran is the most visible and most likely threat. … But what happens if Pakistan really goes sour?" he said, or if Iran gets a nuclear weapon and starts a new arms race in the Middle East?

But U.S. and Israeli military officials downplayed current events, saying that the exercise was just one in a series, and had been long in the planning. Also, the Middle East is usually fraught by tensions.

"When is it not?" asked U.S. Navy Rear Adm. John Richardson, commander of the exercise. "This is the fifth in a series of Juniper Cobra exercises, which has consistently enhanced the relationship" between U.S. and Israeli forces, he said. "We want to come away from the exercise with best practices to make ourselves even better."

In fact, the exercise in 2005 was roughly the same size, and was also held amid "rising Middle East tensions," according to newspaper reports at the time. Likewise, officials said then that there was no connection between tensions and the exercise.

"There is absolutely no connection with this exercise and any event in the region," a USAREUR spokeswoman said. "As always, we are interested in implementing lessons learned from training exercises."

U.S. troops, primarily from U.S. Army Europe and the European Command, began arriving in Israel about 10 days ago for the exercise.

"To us, it’s not at [a political] level," said Lt. Col. Kevin Ciocca, commander of the 5th Battalion, 7th ADA, 069th Air Defense Artillery Brigade, based in Kaiserslautern. "We train soldiers."

Ciocca has some 400 troops working on the exercise. For them, he said, it was about operating equipment, readying systems, practicing what they’d do in war.

"Training soldiers and getting them ready for combat, irrespective of the political environment," Ciocca said. "The big event really for us is the opportunity for soldiers training with ships, with aircraft, with coalition forces. These are things we can’t really replicate in Germany."

Near the end of the exercise, he said, his soldiers, who operate Patriot missile systems, would be firing six live missiles to hit targets. The Israelis, he said, would fire four.

There is also U.S. Navy involvement, although far less than news reports have said. Quoting unnamed Israeli defense officials, some reports said that 17 U.S. Navy ships were to be part of the drill. In fact, Richardson said, there was only one: the USS Higgins, a guided-missile destroyer, which will not be firing any interceptor missiles.

Richardson said that new capabilities were being tested this year, although he declined to elaborate further. But in April, about 100 Europe-based personnel took part in a missile defense exercise that for the first time incorporated a U.S.-owned radar system, U.S. X-Band radar.

That system, which was deployed to Israel a year ago and marked the first time U.S. troops were permanently deployed to Israel, is intended to give Israel earlier warning in the event of a missile launch from Iran. The X-Band is situated at Nevatim air base in the Negev Desert, one of the bases involved in the exercise.

The X-Band is designed to detect and track missiles soon after launch. According to Defense News, the system is expected to "double or even triple the range at which Israel can detect, track and ultimately intercept Iranian missiles."

Spring said missile defense is a far better option than retaliation.

"What the American people crave and what the Israelis crave is not retaliation," Spring said. "What they really want is to be protected."

This year’s Juniper Cobra exercise is expected to cost an estimated $10 million to $15 million, said Maj. Daniel Meyers, U.S. Army Europe spokesman.

"Can you put a cost on friendship. Can the partnership capacity that is gained through this exercise be measured in dollars?" he said.