The Macedonian army is taking advantage of Nato's 30-day mission to disarm Albanian rebels by gearing up for all-out war in the autumn, western intelligence sources have warned.

Nato observation teams watched four cargo plane-loads of military hardware and spares arriving in secret flights at Petrovac airport near the capital, Skopje, last week. The sources said the four flights were all from eastern Europe. The shipments followed the arrival several days earlier of a giant Antonov transport plane from Ukraine, carrying what the sources believed were sophisticated Russian-made SA-13 anti-aircraft missile systems. It coincided with signs that the Macedonian interior ministry was preparing special police units and paramilitaries for a new offensive against territory the Albanians believed they had "liberated" from Slav authority. In a further setback to the tortuous peace process, the Macedonian parliament yesterday voted to delay a debate on ratifying a Nato-backed peace plan until Albanian guerrillas stopped "terrorising" civilians. Analysts said there was little the British-led Nato force could do to stop the military deliveries. The Macedonian army's only obligation during Operation Essential Harvest is to stay out of agreed buffer zones separating it from the Albanian rebels of the National Liberation Army. Nato officers nevertheless confirmed that overflights by Sukhoi SU-25 "Frogfoot" bombers by the Macedonians in the north of the country had contravened the government's agreement with the alliance. Intelligence experts fear the Macedonians are trying to purchase a new "retrofit" version of the Frogfoot, complete with Israeli avionics fitted in the former Soviet republic of Georgia. This could permit pin-point accuracy in raids.