On Friday, North Korea said it was pursuing a two-pronged strategy that prepared it for 'both dialogue and sanctions'.

If members of the UN Security Council 'wish to put sanctions first before dialogue, we would respond with bolstering our nuclear deterrence', its letter added.

While the correspondence with the UN indicated North Korea might be ready for further talks on its nuclear programme, North Korea observers have warned that Pyongyang's recent strategy could be its typical one, in which it makes concessions, only to retreat from those promises and return to work on its nuclear and missile programmes.

It pledged in 2005 to dismantle its nuclear programmes in six-nation talks, but those negotiations have been stalled since last year and Pyongyang dropped out of them in April.

The Korean Central News Agency said Pyongyang's letter was written in response to questions from the UN sanctions committee about a North Korean arms shipment seized last month while allegedly on its way to Iran. The weapons, including bazookas and munitions for grenade launchers, were confiscated by the United Arab Emirates from an Australian ship, and the UN Security Council is investigating.

South Korea criticised Friday's statement from North Korea. It said its neighbour's behaviour was intolerable.

'The government will deal sternly and consistently with North Korea's threats and provocations,' said Foreign Ministry spokesman Moon Tae Young.

The criticism came after North and South Korea agreed last month to resume reunions of families divided by the 1950-53 Korean War and normalize commuter traffic between the South and their jointly run industrial park in the North Korea border city of Kaesong.