Already two allied soldiers, including a member of Britain's Special Air Service regiment, have been killed in the operation codenamed "Picnic", said a top KLA commander, while the rebel army itself has lost "dozens of men" as a result of the covert raids.
Speaking from a KLA camp in Babine, between the northern Albanian town of Bajram Curri and the Kosovo border, Shpend Gjocaj revealed that British and American special forces originally entered the Serbian province in the early hours of 21 March, three days before the start of the Nato air strikes against Yugoslavia.
But the Serbs' success at concealing themselves from air attacks had led to a decision to send larger formations deep into enemy territory, said Mr Gjocaj. General Wesley Clark, Nato's supreme commander, gave the order, he said, after consulting Hasim Thaci, the KLA's leader and head of a provisional government declared by the few rebel units left in Kosovo.
Serbian forces have proved adept at using tunnels, natural camouflage and underground hideouts to avoid attack from Allied planes flying at a medium altitude of 16,000ft to minimise the risk of anti-aircraft fire. "We are helping the special forces to get in low and identify where the targets are," said Mr Gjocaj, who is the ethnic Albanians' liaison officer in the rapid training and deployment of KLA troops by US, British and French airborne regiments.
Using the 82nd Airborne Division and other air-mobile forces, the object of the "Picnic" teams has been to find out where exactly in Kosovo the Serbs' 40,000 troops and 300 or so armoured vehicles actually are. So far Nato has dismissed Belgrade's claims that it has already started to withdraw its forces from the stricken province.
The switch in tactics was acknowledged last week by Nato's Major-General Walter Jertz, who referred ob- liquely to "improvements in intelligence gathering", and said the alliance was now succeeding in attacking targets identified by "spotter" missions. He declined to comment on KLA reports that Western soldiers had been killed behind enemy lines.
The Ministry of Defence said an SAS sergeant had been killed in a road accident in Bosnia, but TTU-Europe, a French newsletter specialising in defence issues, reported that an SAS soldier was lost behind Yugoslav lines in Kosovo on 26 April.
According to KLA sources, the "Picnic" teams were again flown into Kosovo by helicopter last Monday, crossing the border with Macedonia and landing in the rubble of Malisevo, a town in the Drenica valley formerly occupied by the KLA and proclaimed a liberated capital of "free Kosovo", but later destroyed by the Serbs. The units, made up of 20 to 30 Allied soldiers and up to 100 KLA, moved west towards the villages of Klina and Rugove, near Pec, then towards Prizren, and finally right up to the border with Albania.
A senior KLA commander, who goes by the name of Drini, said the missions were supposed to be what the US Army calls "sterile", which meant the soldiers either wore uniforms that could not be traced to any Allied unit or were disguised in the combat fatigues of the "Black Hand" Serb paramilitaries.
Known for internal divisions and for a lack of self-discipline, the KLA appears to be struggling with the special forces' legendary code of secrecy, however. "Outside Urosevac, we found abandoned barracks, concrete- reinforced bunkers, and a tank base acres in size," Drini said, speaking from central Kosovo by telephone. "When you see such a blatant example of the Serb presence, you scream and beg to get somebody to go in there and blast them."
What Drini and his cohorts want most of all, he says, are strikes by the American fleet of 24 Apache helicopters, each of which carries 16 Hellfire anti-tank missiles with a range of five miles. Nato has been slow to deploy the helicopters (one of which crashed on a training exercise shortly after arriving in Tirana, while another went down 10 days ago, with the loss of its two American pilots).
Voicing his impatience at the deployment of the Apaches and a lethal form of artillery known as Multiple Launch Rocket Systems, whose showers of "steel rain" are capable of killing large numbers of Serb troops on the ground, Drini said: "We have been told these carpet bombing attacks are totally devastating, that nothing can survive."
The MoD said it was aware of reports but never commented on SAS activities. Military analysts say the covert ground offensive is intended to signal to Belgrade that Nato's political leadership, while pressing for peace, is willing to take risks so far avoided in what has been exclusively, and frustratingly for military strategists, an air war.