Istanbul, Rabi'II 10, 1437, January 20, 2016, SPA -- US President Barack Obama and his Turkish counterpart Recep Tayyip Erdogan held a phone call ahead of visit to Istanbul this week by Vice President Joe Biden, Turkey's state-run Anadolu news agency reported, according to dpa. The agency said the call took place late on Tuesday night and focused on terrorism concerns, including last week's suicide bombing in Istanbul which killed 10 German tourists. Biden is due to visit Turkey on Friday and Saturday and is scheduled to meet both Erdogan and Prime Minister Ahmet Davutoglu. --SPA 14:04 LOCAL TIME 11:04 GMT www.spa.gov.sa/w