Nuclear threats from North Korea, including the possibility of an additional nuclear test, will be a key topic when President Park Geun-hye holds talks with U.S. President Barack Obama later this week, an official said Thursday.

Obama is scheduled to arrive in Seoul on Friday for a two-day visit amid growing concerns that Pyongyang could conduct its fourth nuclear test. South Korean officials have cited intelligence showing that all technical preparations have been completed at the Punggye-ri test site.

The trip is overshadowed by the deadly sinking of the ferry Sewol that left nearly 300 people, mostly high school students, dead or missing. While here, Obama is expected to have a chance to express his condolences, Seoul's senior presidential foreign affairs secretary Ju Chul-ki said.

Ju declined to elaborate, referring queries to U.S. officials.

Earlier this week, Ben Rhodes, deputy national security adviser for strategic communication, told reporters in Washington, D.C. that Obama will "want to find a way to express to those families and to the people of the Republic of Korea how much we support them in this difficult time."

After arriving from Japan, Obama is scheduled to hold talks with Park on Friday afternoon.

North Korea issues, including the recent signs of preparations for a nuclear test, will be discussed at the summit, along with the direction of the alliance between the two countries and the situation in Northeast Asia, Ju said.

"The upcoming summit will serve as an opportunity to further solidify the Korea-U.S. alliance amid the grave security situation on the Korean Peninsula and reaffirm watertight cooperation on North Korea in response to threats from the North's nuclear program," he said.

Last month, North Korea threatened to conduct a "new form of nuclear test," apparently referring to a nuclear device built with enriched uranium. The North detonated plutonium-based devices in its three nuclear tests in 2006, 2009 and 2013.

South Korean officials said this week that there has been a lot of activity at North Korea's Punggye-ri nuclear test site and that the North is believed to have completed all preparations, including the removal of a large screen set up to hide the entrance of a tunnel leading to the underground testing place.

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 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)