Before delivering his speech, Trump will hold 10-minute talks with parliamentary leaders, including Assembly Speaker Chung Sye-kyun, vice speakers, and the floor leaders of the ruling and opposition parties.

Trump is expected to be accompanied by top aides, such as Secretary of State Rex Tillerson, National Security Advisor H. R. McMaster and Chief of Staff John Kelly.

"The overall outline of his schedule here has come out based on the (results of) working-level discussions (with the US side)," the source told Yonhap News Agency over the phone, declining to be named. "We will finalize details through additional discussions."

North Korea's escalating nuclear threats are expected to be a focus of Trump's speech, observers said. His visit to Seoul comes amid rising military tensions triggered by Pyongyang's provocations, including its Sept. 3 nuclear blast and a slew of missile tests.

The parliament has not allowed any civilian to attend the speech, apparently for security reasons. It has also requested that lawmakers come to the legislature's main chamber 10 minutes prior to Trump's speech and wear their lawmaker badges for personal identification.

Since 1960, a total of five US presidents, including Bill Clinton, have spoken at the assembly, touching on the changing contours of security and geopolitics following the Korean War, the Vietnam War and other consequential historical events.

The common thread running through their speeches was America's firm commitment to its Asian ally's security and free democracy -- anchored on the 1953 mutual defense treaty -- in the face of persistent threats from the communist North. (Yonhap)