A CRIMINAL investigation has been launched in the former Soviet republic of Kazakhstan into senior defence and government security officials who are suspected of illegally selling MiG fighter jets overseas, amid growing allegations that the aircraft were destined for North Korea.

South Korea yesterday expressed "serious concern" over the suspected purchase of 30 Soviet-era MiG aircraft from Kazakhstan by the North Koreans, who are believed to be building up their military, despite intense poverty and a dependency on international food aid. This week the US State Department pledged to monitor the issue "very, very closely."

The scandal is almost certainly connected to an incident in March, less than a week before Nato began its air strikes on Yugoslavia, when a giant Russian AN-124 cargo plane was impounded in Baku, Azerbaijan. On board, it had six partially dismantled MiGs and a crew of 34 technicians.

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Azeri customs officials initially said that the jets were en route to Yugoslavia in violation of the UN arms embargo, arousing speculation that they had unearthed a covert attempt to reinforcing Slobodan Milosevic's air force before the bombing campaign began.

Kazakhstan swiftly admitted to owning the jets - which were more than 30 years old - but there were conflicting reports from the Kazakh government, Russia and Azerbaijan over the aircraft's final destination. Kazakh authorities said they were destined for the Czech Republic; the cargo plane's crew said they were heading for North Korea. The aircraft were eventually released in April and were returned to Kazakhstan a month after being seized.

This week the issue moved forward anew when South Korea's intelligence chief, Chun Yong-taek, said that North Korea was assembling at least 30 MiG-21 fighter planes with parts brought from a former Soviet republic, later identified by officials as Kazakhstan.

The Kazakh president, Nursultan Nazarbayev, has said nothing publicly about the allegations but there is no doubt that they are a source of embarrassment for his Central Asian republic. It has long been forging ties with the West - in particular, the US - to attract investment for his country's potentially lucrative Caspian oil sector and to assert independence from its former masters in Moscow.

The US. State Department said its officials have been consulting with Kazakhstan's government on the suspected MiG sales to North Korea."We have serious concerns about transfers of this kind, and we continue to monitor this case very, very closely," said its spokesman James Rubin.

Mr Nazarbayev ordered a criminal investigation yesterday into possible violations of arms sales regulations by senior security officials. This week he also sacked his Defence Minister, Mukhtar Altynbayev, and the chairman of the national security committee, Nurtai Abykayev, for "blatant violations" of arms trading laws, and ousted several senior officials involved in the mysterious episode in Baku. More heads can be expected to roll.