ments from North Korea, following a tide of rhetoric threatening attacks on the South and hurling insults at him personally, his office said Wednesday. Lee made the remark in New York on Tuesday at a meeting with Korean Americans, Lee's office said.
"Unlike in the past, there will be nothing like aiding and negotiating with North Korea because of menacing remarks," Lee told the meeting.
Lee's U.S. trip includes his first summit with President George W. Bush later this week.
Lee added that he is ready to begin a dialogue with North Korea at any time if it "opens its heart and tries to forge mutually beneficial relations" with South Korea.
Reconciliation between the two sides has been stalled since Lee took office in February with a pledge to get tough on the North.
Unlike his liberal predecessors, who sought detente with North Korea with massive aid and concessions, Lee opposes providing unconditional assistance to the North and calls for its nuclear disarmament as a precondition for economic cooperation.
That stance angered North Korea. Since late last month, it has expelled South Korean officials from a shared industrial complex, test-fired missiles, called Lee a "political charlatan" and "traitor" and threatened to reduce the South to "ashes."
Lee said he is ready to help rebuild North Korea's economy if it gives up nuclear weapons.
"It is South Koreans who, more than anyone else in the world, are heartbroken at the sight of North Koreans suffering and fleeing" their country, Lee said, "However, there is inconvenience between the South and the North as North Korea develops and arms itself with nuclear weapons."
In an in-flight meeting with aides earlier, Lee suggested leasing farmland in Russia's Far East to secure a stable source of food amid soaring international grain prices, saying such a project would also make it easier for South Korea to provide North Korea with food aid.
"In that case, we can also make use of North Korean labor and directly send (food) to North Korea as the shipping distance is short," he said, without elaborating.
The Korean War ended in 1953 with a truce, not a peace treaty, which means the sides are still technically at war. Their relations improved significantly under Lee's two liberal predecessors - former presidents Kim Dae-jung and Roh Moo-hyun.