WASHINGTON (AFP) - The Phoenix lander's analysis of recent soil samples taken on Mars has found possible traces of perchlorate, a highly oxidising substance detrimental to life, Nasa said late Monday. Two separate soil samples were analysed within the last month by two onboard Phoenix instruments, "suggesting one of the soil constituents may be perchlorate," Nasa said in a statement stressing the preliminary quality of the tests. "We are committed to following a rigorous scientific process. While we have not completed our process on these soil samples, we have very interesting intermediate results," said Peter Smith, Phoenix's principal investigator at the University of Arizona, Tucson. "Initial ... analyses suggested Earth-like soil. Further analysis has revealed un-Earthlike aspects of the soil chemistry," he added. Investigators are working to eliminate any possibility the perchlorate readings in the Martian soil samples were influenced by terrestrial sources coming from the Phoenix spacecraft itself, the National Aeronautics and Space Administration said. The soil samples analysed on Sunday containing a white ice-like substance that when melted turned out to be water - confirming initial suspicions in June - did not contain perchlorate, it added. The soil samples were analysed by the Wet Chemistry Lab of the spacecraft's Microscopy, Electrochemistry, and Conductivity Analyser (MECA), Nasa said. The Phoenix team is also waiting for complementary results from the Thermal and Evolved-Gas Analyser (TEGA), which also is capable of detecting perchlorate, it added. TEGA sniffed the vapour from the ice sample confirming it was indeed water. The Phoenix lander started digging trenches into Martian soil after touching down near the planet's north pole on May 25, revealing a white substance that scientists said was ice in June. Although important nutrients including sodium, potassium and magnesium had been discovered on Mars, no organic materials had been found so far, the Phoenix team said.