The world governing athletics body has asked the Court of Arbitration for Sport (CAS) to double the two-year suspensions imposed on seven female Russian athletes for manipulating doping samples.

A statement by the International Association of Athletics Federations (IAAF) on Friday said an appeal had been filed with CAS against the decision taken by the Russian federation last month.

"The IAAF considers that the offence committed justifies a heavier sanction and requests that the athletes be declared ineligible for a period for four years," the statement said.

Twice world 1,500 metres champion Tatyana Tomashova was one of the athletes banned by the Russian Federation after IAAF testers found that DNA in samples provided in out-of-competition tests in May last year did not match with samples at the subsequent world championships.

World indoor 1,500 metres champion Yelena Soboleva, distance runners Yuliya Fomenko and Svetlana Cherkasova, European discus champion Darya Pishchalnikova, former hammer world record holder Gulfia Khanafeyeva and former world 5,000 metres champion Olga Yegorova were also banned.