ANKARA - Turkey's patience may run out over the crisis in Syria and it could be forced to take action, President Tayyip Erdogan said on Thursday, calling on the United Nations to do more to prevent what he said was "ethnic cleansing" in the country.Erdogan accused the United Nations of insincerity in calling on Turkey to do more to help Syrian refugees instead of taking action to prevent the bloodshed in its southern neighbor."We will show patience up to a point and then we'll do what's necessary. Our buses and planes are not waiting there in vain," he said, adding that Turkey had information that Iran-backed forces in Syria were carrying out "merciless massacres."Turkey, already home to more than 2.6 million Syrian refugees, has long pushed for the creation of a safe zone in northern Syria to protect displaced civilians without bringing them over the border into Turkey.He also said he had previously told the European Union's two top officials, Jean-Claude Juncker and Donald Tusk, that the time could come when Turkey would open the gates for migrants to travel to Europe. Reportedly the same threat was made last week to Tusk, with the demand that Turkey be offered a better deal to deal with the influx.