Seizing control of Syria's al-Bab important to push for Raqqa - Turkish official

ISTANBUL (Reuters) - Seizing control of Syria's al-Bab from Islamic State is important to wiping out the militant group from its stronghold of Raqqa, Turkish President Tayyip Erdogan's spokesman said on Wednesday. Ibrahim Kalin also said the argument that there was no alternative to the Syrian Kurdish YPG militia in the fight against Islamic State was invalid. Turkey is backing a group of Syrian rebels, mainly Arab and Turkmen, in northern Syria against Islamic State and hopes to stop the advance of the YPG, which it sees as a hostile force. The rebels have been besieging the town of al-Bab for weeks. (Reporting by Tulay Karadeniz and Humeyra Pamuk; Writing by Daren Butler; Editing by David Dolan)