Islamabad, Shawwal 4, 1438, Jun 28, 2017, SPA -- A helicopter search for two climbers missing on one of the world's highest mountains started Wednesday in northern Pakistan. The two men - one from Spain, the other from Argentina - were ascending the 8,126-metre-high Nanga Parbat mountain, but fell out of contact at the 6,400-metre mark. Muhammad Iqbal, owner of Summit Karakoram, the tour operating company that arranged the climb, told dpa that he last had contact with the men several days ago. "It is impossible to say what might have happened to them," Iqbal said. "These are very difficult routes." So far, cloudy conditions have made rescue efforts on the mountain impossible. But Iqbal said that bad weather could again stop the search on Wednesday. --SPA 10:50 LOCAL TIME 07:50 GMT www.spa.gov.sa/w437081