By Luke Baker QUNEITRA Golan Heights (Reuters) - U.N. officials shuttled along the rocky frontier between Syria and the Israeli-occupied Golan Heights on Friday, trying to establish the whereabouts of 43 United Nations peacekeepers seized by al-Qaeda-linked militants inside Syria. Israeli forces took up positions at Quneitra, a fortified crossing between Syria and the Golan, barely 400 meters from Nusra Front militants, who attacked a U.N. base on the Syrian side of the border on Wednesday and seized the 43 Fijians.