U.S. President Barack Obama was due in South Korea on Friday for talks with President Park Geun-hye as the Asian ally grieves over the deadly sinking of a ferry while on the lookout for a possible nuclear test by North Korea.

How to deal with Pyongyang is expected to be a major topic for talks between Park and Obama set for later Friday. But attention is also being paid to what action Obama will take to express sympathy and condolences over the Sewol ferry disaster that has left nearly 300 people dead or missing, most of them students.

News reports have speculated that Obama could make a gesture, such as a visit to the mourning altar for the student victims, or announce a package of support measures, to demonstrate U.S. support for one of its biggest allies in Asia.

Obama planned to fly in from Japan for a two-day visit, his fourth to South Korea to make Seoul the president's most visited foreign city. South Korea is the second leg of his four-nation Asian tour that will later take him to Malaysia and the Philippines.

In Tokyo, Obama said he is not optimistic that North Korea will change its behavior in the near future. But he said he is confident that by working with Japan, South Korea and others, the U.S. can apply more pressure so that "at some juncture they end up taking a different course."

Obama also said China's role is "critically important" in dealing with the North.

His talks with Park are also expected to focus on North Korea and its nuclear program as the issue has gained urgency with intelligence suggesting that Pyongyang has completed preparations for what would be its fourth nuclear test.

The North previously conducted nuclear tests in 2006, 2009 and 2013.

Last month, North Korea threatened to conduct a "new form of nuclear test," apparently referring to a blast involving a nuclear device built with highly enriched uranium, its second source of fissile material used for atomic bombs after plutonium.

After the summit, Park and Obama are scheduled to hold a joint news conference where they are expected to issue a strong warning to Pyongyang not to carry out a nuclear test. Obama is also expected to reaffirm the American commitment to South Korea's security.

Other issues on the agenda include ensuring a smooth implementation of the free trade agreement between the two countries and Seoul's request for a further delay in its planned takeover of wartime operational control over its forces from the United States.

A source in Washington said that Obama plans to tell Park that the U.S. has decided to "reconsider" the timing of the OPCON transfer, currently set for 2015, "given changes in security conditions on the Korean Peninsula."

Obama is also expected to mention the decision if asked about it at the joint press conference with Park following their summit. Otherwise, the State Department will issue a separate document on the decision, according to the source.

The announcement would represent an expression of Washington's firm security commitment to South Korea and send a strong message to North Korea at a time of high tensions on the divided peninsula that is still technically at war after the Korean War ended in a truce without a peace treaty.

Enhancing three-way security cooperation between South Korea, the U.S. and Japan, such as by forging a military intelligence-sharing pact, could also be on the table, along with Washington's push for a regional missile defense system.

The U.S. hopes that its two biggest Asian allies -- South Korea and Japan -- will repair their relations that have been frayed badly over issues related to Japan's colonial rule of Korea, and cooperate more closely on security matters, in part to keep a rising China in check.

As part of such efforts, Obama brokered a three-way summit with the South Korean president and Japanese Prime Minister Shinzo Abe last month when the three leaders gathered in the Dutch city of The Hague for an international conference on anti-nuclear terrorism.

That meeting marked the first time that Park and Abe held formal talks since they took office more than a year ago. Despite Obama's efforts, however, there has since been no marked improvement in relations between Seoul and Tokyo.

Obama will bring nine ancient Korean seals with him to return them to South Korea. The national treasures were shipped out of Korea during the 1950-53 Korean War, and their return is seen as a sign of the close friendship between the two countries.

Last November, U.S. customs authorities seized the seals from the family of a deceased U.S. Marine lieutenant who served in the three-year war in Korea. Among them is the Hwangjejibo (Seal of the Emperor) that King Gojong of the Joseon Dynasty (1392-1901) made upon the establishment of the Korean Empire in 1897.

Obama's trip also includes a visit to the War Memorial of Korea, a meeting with business leaders and a visit to the Combined Forces Command at the headquarters in Seoul of some 28,500 American troops stationed in Korea, officials said. (Yonhap)