Amid nascent steps to improve inter-Korean ties, South Korea and the United States may face rifts over North Korean policy, including an approach towards the Gaeseong industrial park, a U.S. congressional think tank said.

 As part of the so-called "trustpolitik," South Korea's conservative Park Geun-hye administration has tried to reach out to North Korea. Pyongyang has responded positively, allowing the temporary reunion this week of families separated by the 1950 53 Korean War.

"An issue for the Obama Administration and Congress is to what extent they will support - or, not oppose - Park's possible inter-Korean initiatives," the Congressional Research Service said in a report posted on its Web site Thursday.

For instance, it pointed out, the Park government has indicated a desire to someday internationalize and expand the Kaesong Industrial Complex, a historic joint venture between the two Koreas located just north of their land border.

"These moves could clash with legislative efforts in Congress to expand U.S. sanctions against North Korea, such as H.R. 1771, the North Korea Sanctions Enforcement Act," it added.

On the Seoul-Washington relations, the CRS said the allies are confronted with tough talks about revising guidelines on their civilian nuclear cooperation.

"One point of disagreement in the renewal process is whether South Korea will press the United States to include a provision that would allow for the reprocessing of its spent fuel," it said.

Seoul also reportedly seeks confirmation of its right to enrichment technology.

"The issue has become a sensitive one for many South Korean officials and politicians, who see it as a matter of national sovereignty," said the CRS.

Still, the U.S. has been reluctant to grant such permission due to concerns over the impact on denuclearization talks with North Korea and on the global nonproliferation regime, it added.

The CRS voiced skepticism that Seoul and Tokyo will find an immediate way to expand their partnerships beyond tentative security cooperation.

"Given the array of domestic forces opposed to raising South Korea-Japan relations to a new level, it is unclear whether the two governments will have the interest or capacity to do more than maintain ad hoc cooperation, such as in response to aggressive North Korean actions," it said.

Meanwhile, a U.S. expert stressed the Obama administration should seek an active role in resolving the drawn-out stand-offs between its key regional allies, mainly over their shared history.

Washington needs to press Tokyo to begin a reconciliation process with Seoul, said Bruce Klingner, senior researcher at the Heritage Foundation.

"This process should include, at a minimum, an unequivocal public affirmation of the Kono and Murayama statements of contrition; a mutually agreed upon mechanism for compensating surviving women forced into sexual slavery during World War II," he said in a report. He was referring to Japan's formal apologies in the 1990s.

Japan's Prime Minister Shinzo Abe will have to promise not to visit Yasukuni Shrine again, he said.

For its part of the process, Klingner added, Seoul should reciprocate by agreeing to a bilateral leaders' summit. (Yonhap News)