By Siva Govindasamy, Alwyn Scott and Tim Hepher KUALA LUMPUR/NEW YORK/PARIS (Reuters) - Investigators trying to solve the disappearance without trace of a Malaysia Airlines jetliner face an extremely rare challenge that could hinder their efforts: they lack the powers of a formal air safety investigation. Malaysian officials are conducting their own informal investigations, in cooperation with other governments and foreign agencies, but they lack the legal powers that would come with a formal international probe under U.N.-sanctioned rules. A senior official familiar with the preliminary Malaysian probe said Malaysian authorities could not yet convene a formal investigation due to a lack of evidence on where - namely, in which national jurisdiction - the Boeing 777-200ER jet crashed. "There have been no issues in getting that information." But Southeast Asian waters are rife with territorial disputes, and any decision by Malaysia to unilaterally open a formal investigation under U.N. rules could be seen as a subtle assertion of sovereignty if the crash site turns out to be inside another country's territory.