US Defence Secretary Mattis says North Korea will witness 'overwhelming' response if it uses nuclear weapons

Unites States President Donald Trump's Defence Secretary John Mattis on Friday warned North Korea of an "effective and overwhelming" response if Pyongyang uses nuclear weapons.

Mattis also assured South Korea of America's steadfast support in protecting its territory from North Korea during his two-day visit to Seoul.

UN slaps North Korea with toughest-ever sanctions to deter nuclear testing

"Any attack on the United States, or our allies, will be defeated, and any use of nuclear weapons would be met with a response that would be effective and overwhelming," Reuters quoted Mattis as saying at South Korea's Defence Ministry.

"North Korea continues to launch missiles, develop its nuclear weapons program and engage in threatening rhetoric and behaviour," he added.

Mattis' statement came amid concerns that North Korea could be readying to test a new ballistic missile. If Pyongyang conducts the test, it could be an early challenge for the Trump administration.

North Korea issues regular threats to destroy South Korea and the United States and conducted more than 20 missile tests last year, which also include two nuclear tests. The nation, in doing so, has defied all the sanctions and resolutions called by the United Nations, causing concern among nations across the world.

In December 2016, the UN had imposed its toughest sanctions against North Korea in an attempt to deter the defiant nation from conducting nuclear missile tests. The sanction is set to put a cap on North Korea's main coal exports, the nation's main external revenue source. The resolution drawn by the nations require North Korea to "abandon all nuclear weapons and existing nuclear programs."

According to reports of the US think tank 38 North, Pyongyang has resumed operation of a reactor at its main Yongbyon nuclear facility, which produces plutonium that can be used for its nuclear weapons program.

North Korea's increasing missile tests have led South Korea and its main ally, the United States, to strengthen their defences. A US missile defence system known as Terminal High Altitude Area Defense (THAAD) is also scheduled to be set up in South Korea later this year. However, China has objected to THAAD saying that it will destabilise the regional security balance.