The United States and South Korea will provide the strongest joint deterrent against North Korea's escalation, said US Special Representative for North Korea Sung Kim amid fears that Pyongyang is preparing to resume nuclear tests, reports Reuters.

US Special Representative Sung Kim and his deputy, Jung Pak, met South Korean officials, including nuclear envoy Noh Kyu-duk, after arriving in Seoul early on Monday for a five-day visit.

"It is extremely important for the United Nations Security Council to send a clear signal to the DPRK that we will not accept its escalatory tests as normal," Kim told reporters after his talks with Noh.

"We agreed on the need to maintain the strongest possible joint deterrent capability on the peninsula," he said.