North Korea made no effort to interfere with a resumption of U.S. Air Force reconnaissance flights off its coast in international airspace, officials said Thursday.

Adm. Thomas Fargo, commander of U.S. forces in the Pacific, told the Senate Armed Services Committee that the reconnaissance missions had resumed Wednesday, but he declined to discuss details of the flights or actions taken to enhance their safety.

Other officials, speaking on condition of anonymity, said the U.S. plane encountered no interference.

The flight was the first since a March 2 incident in which four North Korean fighter jets intercepted an unarmed and unescorted Air Force RC-135S Cobra Ball reconnaissance aircraft over the Sea of Japan about 150 miles off North Korea's coast. It was the first such incident since 1969 and was viewed by the U.S. military as an unjustified and dangerous provocation.

The latest U.S. reconnaissance flight was not escorted by U.S. fighters, but it was monitored closely by airborne and ship radars, officials said.

Asked about the situation at a Senate Armed Services hearing, Fargo said, "We retain our right to fly these unarmed surveillance and reconnaissance flights in international airspace, as we do throughout the world."

Fargo said the military was taking "prudent measures" to protect surveillance planes against North Korean interference.

Asked to elaborate, he said it "implies a full range of things that we can do in terms of making sure we have the right intelligence, situational awareness, warning and procedures in place to ensure that the plane can fly its mission safely."

The United States has always asserted its right to conduct aerial surveillance in international airspace without armed escort, and rarely has encountered hostile interference. The surveillance effort has taken on added urgency in recent weeks as North Korea test-fired two short-range missiles and some believe it is preparing to test a medium-range missile capable of reaching Japan.

Tensions have escalated since North Korea restarted a nuclear weapons program that had been mothballed under a 1994 agreement with the United States. President Bush has expressed confidence that North Korea can be persuaded to abandon the nuclear program peacefully, but he has not ruled out using military force.

The U.S. reconnaissance flights resumed on a day when Bush and South Korean President Roh Moo-hyun discussed the nuclear situation by telephone. White House spokesman Ari Fleischer provided no details beyond reiterating Bush's view that the United States seeks the help of "other countries in the region for a peaceful solution through diplomacy."

The United States uses a variety of intelligence, surveillance and reconnaissance methods to monitor North Korea's military activity, including developments in its nuclear weapons program.

The Air Force RC-135S plane is equipped with multiple electronic receivers. It has large circular windows in the fuselage for the photography of foreign ballistic-missile tests at long range. The intelligence equipment aboard includes multiple infrared telescopes.