WASHINGTON, Feb. 17 (Yonhap) -- Outgoing South Korean Ambassador to Washington Han Duck-soo paid a visit to U.S. Secretary of State Hillary Clinton on Friday as he prepared to end a three-year stint in the job that he said put him under constant pressure over a free trade deal and North Korea.

The farewell meeting with Clinton was set up as the top American diplomat asked for it, sources said. Clinton told Han during the meeting that the envoy did a great job in further strengthening the traditional alliance between the two countries, they said.

Considering it is not common for a South Korean ambassador to meet one-on-one with the secretary of state, Han's meeting with Clinton in her office was seen as exceptional treatment for the top envoy from an ally, an official at the South Korean Embassy said.

Han made a surprise offer to step down earlier this week during a visit to Seoul. A veteran bureaucrat who is credited with helping the landmark free trade agreement pass through Congress in October, Han was named the head of the Korea International Trade Association on Friday.

The envoy came back to Washington on Thursday and has since been exchanging farewell greetings with key U.S. officials and foreign diplomats. He talked by phone with National Security Council Asia director Daniel Russel and Michael Froman, deputy national security adviser for international economic affairs.

After the meeting with Clinton, Han also met with Undersecretary of State for Political Affairs Wendy Sherman. A meeting with Deputy Secretary of State William Burns did not happen as Burns was away on an overseas trip. A meeting with Assistant Secretary of State Kurt Campbell is set for Sunday.

Han also attended a farewell ceremony at the embassy.

"I have never got away from enormous pressure since assuming this ambassador post in March 2009," Han said during a farewell meeting with South Korean correspondents, speaking of the heavy responsibilities as ambassador to Seoul's most important ally.

Han also talked about emergency meetings he held with top U.S.

Officials to discuss strategies in the wake of North Korea's sinking of a South Korean warship in March 2010, and its artillery attack on a South Korean border island in November that year.

On the free trade pact, Han said that an announcement is imminent of when the pact is going to take effect. The deal, first signed in 2007 and modified in 2010, won legislative approval from both nations last year. The two countries have made final preparations to implement it.

"The Korea-U.S. alliance is not something for granted," Han said. "We should not take the Korea-U.S. relations, which form a big pillar in our national security and economic development, for granted."