Work to restart the reactor will begin “without delay,” a spokesperson from North Korea's General Department of Atomic Energy was quoted as saying by the state-run KCNA news agency. The spokesperson also said the move would boost the “quality and quantity” of the isolated northeast Asian state’s nuclear capability.

The move came after North Korean leader Kim Jong-un said on Sunday that developing the country’s nuclear weapons was a top priority and a means of maintaining the fragile peace in the region.

Tensions began to rise on the Korean Peninsula after international sanctions were imposed on North Korea in response to a long-range rocket launch in December that world powers condemned as a ballistic missile test. North Korea responded by carrying out a third nuclear test in February, which was followed by more sanctions.

North Korea threatened pre-emptive nuclear strikes on the US mainland and US military bases in the region last month. The threats came as US and South Korean forces carried out annual joint military drills, including near the maritime border between the two Koreas. The United States responded by deploying F-22 Raptor stealth fighters to the region.

Analysts say North Korea is unlikely to launch a full-scale attack on either US forces or South Korea, but concerns persist that rising tensions could spark hostilities.

Senior Russian Foreign Ministry official Grigory Logvinov said on Tuesday that Moscow believed talks with North Korea over its nuclear program were still a possibility.