The Republic of Korea (ROK) and the United States have agreed that the six-party talks is an \" effective\" way to achieve \"tangible\" progress in denuclearization of the Korean Peninsula, ROK President Lee Myung-bak said here on Thursday. \"Korea and the United States stand united,\" Lee said in his address to a joint session of the U.S. Congress. \"We are in full agreement that the six-party talks is an effective way to achieve tangible progress.\" \"We are in full agreement that we must also pursue dialogue with North Korea,\" he added. \"However, we must also maintain our principled approach, a North Korea policy that is firmly rooted upon such principles as the key that will allow us to ultimately and fundamentally resolve this issue,\" Lee told the U.S. Congress. He said: \"North Korea\'s development is in our collective interest, and this is what we want. However, this depends on its willingness to end all provocations and make genuine peace.\" \"We will work with you and the international community so that North Korea makes the right choice,\" he added. The six-party talks, a mechanism that involves China, the Democratic People\'s Republic of Korea (DPRK), the U.S., the ROK, Russia and Japan, began in Aug. 2003. Six rounds of such talks were held before getting stalled in Dec. 2008, and DPRK quit the talks in 2009. A series of events had taken place since and strained ties between the two sides on the Korean Peninsula. However, DPRK has vowed to continue its cooperation with all the parties concerned for an \"unconditional resumption\" of the six-party talks, and delegates from ROK and the U.S. had met respectively with their DPRK counterparts over renewed talks in the past months. Lee, who is on a state visit to the U.S., held bilateral talks with his U.S. counterpart Barack Obama at the White House earlier in the day.