ANKARA, Oct 15 (Reuters) - Turkey is preparing for possible further military action against a U.S.-backed Kurdish militia in northern Syria if talks on the issue with the United States and Russia fail, two Turkish officials said. President Tayyip Erdogan said this week Ankara was determined to eliminate threats originating in northern Syria and that a Kurdish YPG militia attack that killed two Turkish police officers was "the final straw". read more Turkey said the police in Syria"s Azaz region were hit in a guided missile attack on Sunday launched from Tel Rifaat by the YPG, which Ankara considers a terrorist group closely linked to militants fighting a decades-old insurgency in southeast Turkey. "It is essential that the areas, notably the Tel Rifaat region from which attacks are constantly carried out against us, are cleansed," one senior official told Reuters. Turkish forces have launched three incursions in the last five years, seizing hundreds of kilometres of border strip and pushing around 30 km (20 miles) into northern Syria. Russian jets, Iran-backed fighters, Turkish-supported insurgents, jihadists, U.S. troops and Syrian government forces also operate across the patchwork of territories in northern Syria, as well as the Kurdish YPG. The United States views the YPG as a key ally in the fight against Islamic State in northeast Syria. Russia has forces in the area to support Syrian President Bashar al-Assad. TIMING UNCLEAR The time and nature of any further Turkish military action was unclear. The official said the military and national intelligence agency MIT were making preparations. "The decision for this has been taken and the necessary coordination will be done with particular countries. This subject will be discussed with Russia and the United States," he added. The officials said Erdogan would discuss the issue with U.S. President Joe Biden at a G20 summit of the world"s major economies in Rome at the end of October. Another official said the YPG must be pushed back at least 30 km, noting Russia was completely in control of the areas from which recent attacks had come, along with some Iranian elements. Erdogan will speak with Russian President Vladimir Putin after the talks with Biden, he said. "If there is no outcome from diplomacy and the PYD does not leave these areas, an operation appears unavoidable," he said, using the abbreviation for the YPG"s political wing and referring to Tel Rifaat and "several other locations". On Monday, shells believed to have been fired from a YPG-controlled area east of Tel Rifaat exploded in the Turkish town of Karkamis, across the border from Syria"s Jarablus, causing slight damage, Turkey said. Azaz and Jarablus have been under the control of rebels backed by Turkey since Ankara"s first incursion into Syria in 2016 - an operation that aimed to drive Islamic State militants and the YPG away from the border. Since then Ankara has launched two other operations in Syria against the YPG, one targeting the northwest Afrin region and one further east.