Key Iraq-Syria crossing ?falls to IS? Islamic State militants have seized the last Syrian government-controlled border crossing between Syria and Iraq, a Syria monitoring group says.Government forces withdrew from al-Tanf - k**wn as al-Waleed in Iraq - crossing as IS advanced, the Syrian Observatory for Human Rights (SOHR) said.The loss of al-Tanf to IS follows the group's takeover of the ancient Syrian city of Palmyra on Thursday.The US says that fighting the militants will be a "difficult challenge".