US Secretary of State Rex Tillerson has given assurances that Washingtons only goal in Syria is fighting ISIS, the TASS news agency cited Russian Foreign Minister Sergei Lavrov as saying on Thursday. Lavrov said he had last had a telephone conversation with Tillerson on Oct. 9, the agency reported. Russias defense ministry accused the United States on Tuesday of pretending to fight ISIS and of deliberately reducing its air strikes in Iraq to allow the groups militants to stream into Syria to slow the Russian-backed advance of the Syrian army. Lavrov, touching upon a possible US withdrawal from the Iran nuclear deal, said it was hard to imagine how it could be legally implemented, TASS reported.