* Spanish rider provisionally suspended
* Contador blames food contamination
* Tour of Spain runner-up also fails test
* Italian police seize tablets at cyclist's home
The suspensions set back the sport's efforts to restore its credibility after a string of high-profile drugs cases.
"It tugged at my heartstring when I heard the news (about Contador). Such scandals don't do the sport any good. Especially for the sponsors, who try to avoid such bad publicity," Francis Lafargue, head of communications at Team Caisse d'Epargne, told Reuters.
Contador, one of the biggest names in cycling, tested positive for a "very small concentration" of a banned anabolic agent and was provisionally suspended, the sport's governing body, the International Cycling Union (UCI), said. It added in a statement that the Spaniard, who won his third Tour this year, was tested during the second rest day of the highest profile race in the cycling calendar.
Contador, regarded as one of the sport's greatest ever riders, vehemently denied doping, telling a news conference that contaminated meat was to blame for the positive result.
Shortly afterwards, the UCI revealed that Mosquera, second in another of the sport's blue riband races, the Tour of Spain, had also tested for a banned substance which helps increase blood volume delivering oxygen to the body.
His Xacobeo team mate and fellow-Spaniard, David Garcia Da Pena, failed a test for the same substance, hydroxyethyl starch, the UCI said.
Contador's news, however, was by far the bigger blow to cycling and its most famous race, with a second B test confirming the presence of clenbuterol, a banned steroid.
"The rider, who had already put an end to his cycling season before the result was known, was nevertheless formally and provisionally suspended as is prescribed by the World Anti-Doping Code," the UCI statement said.
Contador, who is leaving Astana to join Bjarne Riis's Saxo Bank team next season said he was "sad and disappointed" and the case was "a genuine mistake".
"It's such a small quantity that it's impossible to ingest or administer to yourself and in terms of performance, it doesn't help at all," he said.
"I won't allow something like this to ruin everything. It won't be easy but I don't think it will affect me."
Saxo Bank said in a statement: "It is Riis Cycling's hope that this case can be resolved in a orderly and timely fashion as it is in the best interests of all parties involved that the proper conclusions are drawn within a reasonable period of time.
"The team has had and will continue to have the position that cheating of any form will not be tolerated."
Clenbuterol can be abused by athletes to strip fat and enhance muscle size and can have short-term stimulant effects including increasing aerobic capacity, blood pressure and alertness. It has led to bans for cyclists in the past.
The concentration in Contador's A test was "400 time(s) less than what the antidoping laboratories accredited by (World Anti-Doping Agency) WADA must be able to detect," the UCI said in a statement.
"In view of this very small concentration and in consultation with WADA, the UCI immediately had the proper results management proceedings conducted including the analysis of B sample that confirmed the first result."
The case would require "further scientific investigation" before any conclusion could be drawn and could take some time, the statement added.
On a dark day for world cycling, a source close to an investigation in Italy said police found 50 unidentified tablets at the home of Italian cyclist Riccardo Ricco during a probe into doping. He was not under formal investigation, the source said.
The finding clearly puts 27-year-old Contador's Tour de France victory in July with Kazakh-funded Astana under a cloud and threatens to leave an indelible stain on the Spaniard, who also won the 2007 and 2009 Tours.
"Sincerely I am not worried that people will doubt my result at the Tour de France as in this quantity (the substance) is insignificant when trying for any kind of improvement," Contador said.
The Contador and Tour of Spain findings have cast a pall over the road world championships in Australia's port city of Geelong this week.
The Spanish team at the championships, where the men's time trial world title was being decided on Thursday, declined to comment.
Floyd Landis, the 2006 Tour de France winner whose victory was later shown to be drugs-fuelled, has claimed that the sport is riddled with doping and that its highest-profile rider, seven-times Tour winner Lance Armstrong, has also cheated.
Armstrong has consistently denied this and never failed a doping test.