US Defense Secretary Leon Panetta embarks Sunday on a tour of Asia to take the pulse of key allies as Washington prepares for rare direct talks with North Korea over its nuclear program.

In his first trip to the region since taking the helm at the Pentagon in July, the former CIA director will begin with a stop in Indonesia at the weekend before heading to Japan on Monday and South Korea on Wednesday.

The trip coincides with sensitive direct talks between the United States and North Korea in Geneva next week to try to lay the ground for reviving long-stalled nuclear disarmament negotiations.

Before any broader discussions, the United States and South Korea are insisting the North take concrete steps to demonstrate it is sincere about resuming the full six-party nuclear dialogue with Japan, Russia and China.

In meetings in Tokyo and Seoul, Panetta "will have an opportunity to discuss with his counterparts where we are in the diplomatic process," a senior defense official said.

The defense chiefs will examine what steps to take to bolster diplomacy, but also insure that they are prepared, should North Korea "choose to undertake a provocation," said the official, who spoke on condition of anonymity.

"We are essentially exploring the proposition and trying to ascertain if the North Koreans are serious about engaging in nuclear diplomacy and serious about living up to their commitments under the six-party process," the official said.

In April 2009, the North formally quit the six-party forum, a month before staging its second atomic weapons test. In 2010, Pyongyang torpedoed and sank a South Korean ship and unleashed an artillery barrage on a South Korean island.

"If they are serious, and they are willing to take concrete steps, then there's a clear path back towards the six-party process and diplomacy," the defense official said.

"But that yet has to be seen."

Apart from diplomacy focused on North Korea, Panetta's talks in Tokyo are expected to cover missile defense plans, potential US arms sales and the controversial future of the US Futenma air base on the island of Okinawa.

The Pentagon chief travels to Seoul on Wednesday for a two-day stop with US-South Korean relations at a high point, after President Lee Myung-Bak's red carpet treatment this month in Washington and the approval of a free-trade agreement between the two countries.

Panetta was scheduled to meet Lee, Foreign Minister Kim Sung-Hwan and his counterpart, Kim Kwan-Jin, after South Korean and US forces staged a major joint exercise this week over the Yellow Sea that simulated dogfights with North Korea.

Before Japan and South Korea, Panetta will start his trip on the Indonesia island of Bali, where he is due to arrive Saturday before meetings with Defense Minister Purnomo Yusgiantoro to discuss maritime security and reforms in the country's military, another defense official said.

The United States last year resumed ties with Indonesia's special forces after a 12-year suspension following military reforms and pledges from Jakarta to safeguard human rights.

The Pentagon chief also will hold talks with defense ministers from the Association of Southeast Asian Nations (ASEAN) on the sidelines of the bloc's meeting in Bali.

Disputes between ASEAN members and China over the resource-rich South China Sea will likely feature high on the agenda, as Washington has called for a regional code of conduct and insisted on "freedom of navigation" through the crucial global shipping route despite Beijing's territorial claims.

China says it has sovereignty over essentially all of the South China Sea, where its professed ownership of the Spratly archipelago overlaps with claims by Vietnam, the Philippines, Taiwan, Brunei and Malaysia.