Patrick Shanahan will take over as acting secretary to cover the accelerated departure.
The area will be established by Oct. 15 and be 9 to 12 miles deep, with troops from Russia and NATO-member Turkey conducting coordinated patrols.
Iranian and Russian leaders support a military campaign to retake the last rebel-held stronghold in Syria as Turkey's president pleads for a cease-fire. U.S. and others warn of a bloody humanitarian disaster.
Regime media paints a modern, Western-friendly picture, while opposition media depicts women as passive and dependent. Emerging news outlets are trying to present a more accurate image.
Syria's military claims the jet was targeted by Israel over Syrian territory as it flew sorties against Islamic State militants. Meanwhile, Syrian forces reach the border fence at the edge of the Israeli-occupied Golan Heights.
The country has suffered catastrophic damage, and aspects of the seven-year conflict are far from over. However, the government now controls major opposition strongholds and key cities.
The capture of the crossing reinstates sovereignty over a key region, potentially opening the way for Syrian exports to Arab countries, and is another victory for President Bashar Assad.
Israel wishes to keep Iran, a Syrian ally, as far away from its border as possible—along with Iran's proxy, the Lebanese militia Hezbollah.
With the capture from Islamic State militants of an enclave in southern Damascus, the city and its suburbs are now in the hands of Syrian President Bashar Assad for the first time since 2011.
The death toll includes 19 Iranians, raising fears that the region may be sliding into an unprecedented direct confrontation between two archenemies.