The ISIL affiliate in Sinai is of most concern to the US government following that in Libya, according to testimony by US Special Presidential Envoy for the Global Coalition to Counter ISIL Brett H. McGurk in his testimony (pdf) to the US Senate Foreign Relations Committee on Tuesday. “We assess [Wilayat Sina] was responsible for destroying the civilian Metrojet airliner nine months ago… We estimate its manpower to be from several hundred up to 1,000, with some estimates far less than that, and some slightly more… The Egyptian Army has increased combat operations and closed almost all the tunnels that facilitated arms smuggling along the Gaza border… The Sinai security situation also impacts the Multi-National Forces and Observers (MFO) mission. The US is firmly committed to supporting the Treaty of Peace and MFO operations.”