North Korea says it has restarted its main nuclear complex and is working to improve its nuclear weapons "in quality and quantity".
In comments carried on the country's official KCNA news agency, the director of the North's Atomic Energy Institute said the country was full ready to respond to US hostility with "nuclear weapons any time".
The Yongbyon nuclear plant - which produces fissile material used in the nuclear weapons programme - was closed in 2007, with plans for a revamp announced in 2013.
North and South Korea have reached an agreement following two days of talks to end hostilities between the two sides.
Under the accord, North Korea expressed regret over a landmine incident that wounded two South Korean soldiers earlier this month. South Korea, in return, agreed to stop anti-North propaganda broadcasts along the border from midday tomorrow.
In a joint statement, the two sides agreed to hold follow-up talks aimed at improving ties. North Korea has ended the "quasi-state of war" it had declared.
Last week an exchange of artillery fire across the border had pushed the Korean peninsula to the brink of armed conflict.
"It is very meaningful that from this meeting North Korea apologised for the landmine provocation and promised to work to prevent the recurrence of such events and ease tensions." Kim Kwan-jin, South Korea's national security adviser said in a televised statement.
North and South Korean officials have struck a deal after negotiations to end tensions on the peninsula.
South Korea is expected to announce a joint statement on the agreement with North Korea shortly.
South Korea's anti-North propaganda broadcasts will continue to be blared across the border unless Pyongyang apologises, the country's president has said.
Park Geun-hye said the South deserved an apology after two South Korean soldiers were wounded by landmines along the border.
A statement released by her office reveals Park reportedly told her top aides:
We need a clear apology and measures to prevent a recurrence of these provocations and tense situations.
Otherwise, this government will take appropriate steps and continue loudspeaker broadcasts.
It comes amid lengthy inter-Korean talks aimed at easing tensions that have brought the peninsula to the brink of armed conflict.
In 2004, North and South Korea agreed to stop blaring propaganda at one another across the border, but such broadcasts have resumed in recent days as relations between the two countries deteriorate.
Senior aides to the leaders of North and South Korea are continuing talks aimed at easing tensions that have brought the peninsula to the brink of armed conflict.
The meeting at the Panmunjom truce village began on Saturday evening, shortly after North Korea's deadline for loudspeaker propaganda broadcasts along the border to stop or face military action.
The envoys, shown on TV exchanging handshakes at the start of their meeting, are discussing ways to resolve tensions and improve ties, South Korean officials said.
Talks aimed at ending a standoff between North and South Korea are due to continue tomorrow after being adjourned for the day.
The talks, which have seen top aides to the leaders of both countries meet in an attempt to defuse mounting tensions and try to avert possible military action, are being held at the Panmunjom truce village.
According to South Korea's presidential spokesman Min Kyung-wook the meeting adjourned at 4.15am but will resume at 3pm on Sunday. No details about the talks have been disclosed.
Top aides to the leaders of North and South Korea have agreed to "hold contact" after talks aimed at ending a standoff between the two countries.
The meeting was held at the Panmunjom truce village after an exchange of artillery fire on Thursday strained relations between the two sides.
North Korea had issued an ultimatum with a deadline demanding that the South halt its loudspeaker propaganda broadcasts along the border or face military action.
That deadline passed without any reported incidents.
"The South and the North agreed to hold contact related to the ongoing situation in South-North relations," Kim Kyou-hyun, South Korea's deputy national security adviser, said in a televised briefing.
Top aides to the leaders of North and South Korea will meet at the Panmunjom truce village close to the military border on Saturday to discuss the situation on the Korean peninsula, the South's presidential office said.
It comes amid high tensions following an exchange of artillery fire on Thursday.
The meeting is due to take place half an hour after North Korea's previously set ultimatum demanding that the South halt its loudspeaker propaganda broadcasts along the border or face military action.
North Korea says it will move its troops into a "wartime state" after a recent exchange of fire with neighbouring South Korea.Read the full story ›