The U.S. intelligence chief said on Monday that the DPRK has probably conducted a nuclear explosion last month.

"The U.S. Intelligence Community assesses that North Korea probably conducted an underground nuclear explosion in the vicinity of P'unggye on May 25, 2009," said Director of National Intelligence Dennis Blair in a brief statement.

"The explosion yield was approximately a few kilotons," he added.

According to U.S. media reports, U.S. intelligence officials have warned President Barack Obama that the DPRK would conduct another nuclear test in response to the toughened sanctions arrived at by the UN Security Council for the May 25 nuclear test, DPRK's second since October 2006.

The statement also came as South Korean President Lee Myung-Bak arrived in Washington, D.C. on Monday for talks Tuesday with Obama.