SEOUL, March 21 (Xinhua) -- Top U.S. nuclear envoy in the six-party talks to denuclearize the Korean Peninsula planned to meet key South Korean presidential contenders during his four-day visit to Seoul.

Joseph Yun, the U.S. special representative of the State Department on the Democratic People's Republic of Korea (DPRK) policy, met at a restaurant in Seoul Tuesday with South Chungcheong province governor Ahn Hee-jung of the biggest opposition Minjoo Party of South Korea.

An official with Ahn's election campaign office said via text message that Ahn met with Yun for about an hour to exchange views on various issues including the DPRK's nuclear program and the U.S.-South Korea relations.

Ahn is one of the three major Minjoo Party presidential hopefuls together with former Minjoo Party chief Moon Jae-in and Seongnam city mayor Lee Jae-myung.

The U.S. envoy arrived here late Monday after visiting China. Yun, who represents the United States in the six-way dialogue to denuclearize the peninsula, is scheduled to stay in Seoul until Thursday.

The six-party talks, which involve the two Koreas, China, the U.S., Russia and Japan, have been suspended since late 2008.

On Wednesday, the U.S. diplomat will meet with security and diplomacy advisers to Moon, the current frontrunner in recent opinion surveys who lost to former President Park Geun-hye in the 2012 presidential election, according to Yonhap news agency report.

A presidential election is slated to be held on May 9 as the constitutional court upheld a motion to impeach Park on March 10. The by-election is required to be held in 60 days after a president is unseated.

Earlier in the day, Park appeared in the prosecutors' office to be questioned over a corruption scandal that led to her impeachment and ouster.

Meanwhile, Ahn Cheol-soo of the minor opposition People's Party is considering whether to have a meeting with the U.S. envoy if his schedule is allowed. The software tycoon-turned-politician is a key presidential hopeful of the party.