South Korea has said it will become a full member of a US-led initiative to curb trade in weapons of mass destruction (WMD), a day after North Korea conducted its second nuclear test.

In a short statement on Tuesday the foreign ministry in Seoul announced it was formally joining the Proliferation Security Initiative (PSI) - a move North Korea has previously said it would view as "an act of war".

The announcement comes amid a sharp rise in already tense relations on the Korean peninsula following North Korea's second nuclear test.

South Korea has so far been an observer in the PSI for fear of offending its communist neighbour.

However the foreign ministry said it had decided to become a full member after North Korea launched a rocket on April 5, although it had delayed a formal announcement while trying to resume dialogue with the North.

South Korea's Yonhap news agency quoted government officials as saying that there was no reason to wait any longer following Monday's test.

'Grave threat'

North Korea's missiles and related technology provide much-needed revenue [AFP]

He did not mention Monday's test.
 
The PSI initiative, which includes military drills, was launched by George Bush, the then US president in 2003.

Tuesday's announcement marks the end of a drawn-out debate in Seoul whether to join the largely symbolic naval exercise that brings together nearly 100 countries.

South Korean officials have said that joining the PSI would allow them better access to intelligence concerning the North's flow of WMDs and related technology.

North Korea has been a leading exporter of missiles in recent years, shipping weapons systems to several countries including Pakistan, Iran, Yemen, Syria and Libya in return for much needed hard currency.

It is also thought to have exchanged missile technology with scientists involved in Pakistan's nuclear programme.