A spokesman at North Korea's foreign ministry warned that armed with nuclear weapons, North Korea is prepared to counter what it calls Washington's attacks in a bid to make the US face a miserable end.

"In case a war breaks out on the Korean Peninsula, the US will be held wholly accountable for it, no matter who will launch a pre-emptive attack, as it is causing trouble by bringing lots of nuclear strategic assets and special warfare means...," the spokesman was quoted as saying by the Korean Central News Agency.

The North showed a sensitive reaction against special operation drills by South Korea and the US, which are known to be aimed at eliminating the North's leadership in case of war.

South Korean and US special operations forces, including the US Navy SEAL team that killed Osama bin Laden, are joining the allies' joint military exercises for the first time.

The warning came amid growing signs that North Korea is likely to conduct its sixth nuclear test in defiance of international condemnation. Pyongyang carried out two nuclear tests last year alone following those in 2006, 2009 and 2013.

North Korea has insisted that its development of nuclear weapons is a deterrent against what it calls Washington's hostile policy toward it.

Friday will mark the fourth anniversary of North Korea's announcement that the country will adopt the dual pursuit of nuclear and economic development, commonly known as "byeongjin policy," as its official policy line.

The Rodong Sinmun, the main organ of the ruling Workers' Party of Korea, said that the country's nuclear deterrent has reached its "highest level."

At a rare congress by the WPK in May last year, North Korean leader Kim Jong-un pledged to "permanently" seek his signature dual policy. (Yonhap)