MONTE CARLO, Monaco - Mercedes and Pirelli are under pressure to explain why Mercedes was allowed to conduct in-season tyre-testing after the Spanish F1 GP two weeks ago. Rival team Red Bull launched an official protest just before the start of Sunday's Monaco GP.Red Bull team principal Christian Horner said: "We feel it's not in line with the rules - that's why we've protested before the race. We just want clarity."Mercedes had been lightning-fast in qualifying, securing a fourth consecutive pole start for Monaco but had yet to win a race in 2013 as it struggled with durability in races.'NO WRONGDOING'Pirelli, in agreement with Mercedes, conducted tyre tests after the Spanish GP, something not permitted under the sport's rules. However Pirelli insists its contract allows it to conduct private tests with individual teams under special circumstances.F1's governing body has yet to comment but Pirelli's head of motorsport, Paul Hembery, believes there is no wrongdoing.Hembery said before Sunday's race: "It's completely regular in that we are allowed to do a 1000km tyre test with any team. It's exactly the same in the World Rally championship contract. We can do it with a representative car. We've done it before with another team and we've asked another team to do some work as well."Hembery said the testing was to look at possibilities for developing 2014's tyres - providing Pirelli was still the official manufacturer - and in no way gave Mercedes any advantage in Monaco."Absolutely not, It has no relevance to what's happening here," he said. "Mercedes hasn't a clue what we were testing."GREEN LIGHTNiki Lauda, Mercedes GP's non-executive chairman, added on SkySports TV that the FIA gave permission for the tests. "We asked the FIA 'Are we allowed to do this?' The FIA confirmed it and said 'yes' so we did the test. "These tests can always come in cases of emergency, so Mercedes did absolutely nothing wrong."Horner was unhappy that the testing took place at all. "First of all we need to deal with it through the proper channels, and that's what we'll look at doing," he said. "It's a situation on which we need clarification and we are going to request that clarification."Pirelli has been under pressure in recent weeks because of the fast-degrading nature of its tyres - with nearly 80 pit stops at the 2013 Spanish GP. Red Bull, led by Horner and championship leader Sebastian Vettel, has been one of the most fierce critics of the Pirelli tyres and the manufacturer still does not have the backing of all teams - or any word from the FIA - over a new contract for the 2014 season. Pirelli responded to the criticism over the weakness of its tyres by recently pledging to make modifications for the Canadian GP in June 2013.The fact that Mercedes has been struggling for race pace, and that Pirelli has been trying to improve the resistance of its tyes, seemingly gives extra meaning to the private testing.POLE DEBATABLE"Irrelevant of what you call it, that's testing," Horner said. "They've both cars on the front row of the grid, so it's not hurt."However, Mercedes has been fastest in qualifying for four consecutive races so it is debatable whether the testing would have made any difference to gaining pole in Monaco.Vettel was third-fastest in qualifying and started ahead of Webber, 2012's Monaco GP winner.Red Bull has won the past three Monaco GP races. Stay with Wheels24 for the 2013 Formula 1 season – fresh reports every day.