UEBERLINGEN - Swiss air traffic control faced further questions on Thursday after officials revealed its radar had failed to meet European standards, just a week before a mid-air collision killed 71 people.

The head of the Swiss Federal Bureau for Aircraft Accident Investigations, Jean Overney, said a report a week ago into the radar's shortcomings was severe enough for improvements to be ordered to bring it into line with standards set by Eurocontrol, the European agency in charge of tracking aircraft in flight.

The revelation on Swiss Television late on Wednesday may add to pressure after it emerged a collision warning system at Zurich was switched off and a controller was taking a break when a Russian charter carrying dozens of children collided with a DHL cargo jet over southern Germany late on Monday night.

Russian officials have already expressed anger at initial suggestions that the pilot of the Tupolev 154 may have been to blame. His employers, Bashkirian Airlines, have accused the Swiss of causing the crash over the German-Swiss border. The pilot had only 50 seconds warning of the approaching Boeing 757.

Some 140 grieving Russian relatives were expected in the resort town of Ueberlingen on the shore of Lake Constance on Thursday. Some may help identify bodies, including those of 52 children and teenagers who were going on holiday to Spain.

Swiss investigator Overney told Swiss Television the radar problems "were severe enough that we told them to improve it so that the reduced vertical separation minimums that have been introduced can be (implemented) with sufficient safety".

New rules that took effect in Europe this year reduced the vertical distance that aircraft must maintain from each other to 1,000 feet (300 metres) from 2,000.

Overney said the report's findings were not contested by Skyguide, the Swiss air traffic control agency.

He did not specify which parts of the Swiss radar fell below Eurocontrol standards but a Swiss Television report said the location of aircraft on Swiss controllers' screens updated every 12 seconds instead of the recommended eight.

NO BEARING ON CRASH

Carlo Bernasconi, head of operations for Skyguide, said the report's recommendations had no bearing on Monday's crash - with the possible exception of the screen update standard. An eight-second delay might have allowed the controller to warn the Russian jet to veer up to four seconds sooner, he told Swiss TV.

Skyguide officials acknowledge the 50-second warning was cutting it close but insist it was within acceptable limits. They also say it took 25 seconds for the Russian pilot to react.

Both jets were diving in a vain attempt to avoid one another when they crashed in mid-air and exploded.

The relatives, mostly from the mainly Muslim Urals region of Bashkortostan, face the prospect of identifying corpses that rescuers say are in some cases mutilated beyond recognition.

"It is now our most important task to recover the bodies," Thomas Schaeuble, the interior minister of the German state of Baden-Wuerttemberg, told a news conference on Wednesday. "We hope to be able to complete the recovery of bodies tomorrow."

So far the only victims identified are the two pilots of the DHL Boeing. Police say 38 bodies in all have been recovered.

Officials said that because of a lack of hospital space they would store bodies for now in a network of naturally cooled underground tunnels built for armaments firms in World War Two by slave labourers from the Nazis' Dachau concentration camp.

BRING PHOTOS, PARENTS TOLD

Germany's Foreign Ministry said visas were being issued immediately for mourners wishing to visit the crash site now. Others travelling later would be granted a visa on arrival, an exception to the rules, a spokesman said.

Russian television said government offices had speeded up procedures to ensure all relatives had valid passports. It also said many relatives wanted the victims placed in a common grave.

German officials sent the relatives a list of suggested items to help them identify the victims, including photographs, clothing, dental and medical records and blood groups.

German police have taken over a school gymnasium in another small town near the crash site, Frickingen, and have lined up 15 suitcases found among the wreckage of the Tupolev.

They included typical summer holiday items: a girl's hair clasp, a single new beach sandal, a Russian guidebook to Spain, someone's birth certificate, a case for sunglasses.