The Muslims had conquered Byzantine Armenia in 638–639. Persian Armenia, north of Azerbaijan, remained in Persian hands, along with Khurasan. Umar refused to take any chances; he never perceived the Persians as being weak, which facilitated the speedy conquest of the Persian Empire. Again Umar sent simultaneous expeditions to the far north-east and north-west of the Persian Empire, one to Khurasan in late 643 and the other to Armenia. Bukair ibn Abdullah, who had recently subdued Azerbaijan, was ordered to capture Tiflis. From Bab, on the western coast of the Caspian Sea, Bukair continued his march north. Umar employed his traditional successful strategy of multi-pronged attacks. While Bukair was still kilometres away from Tiflis, Umar instructed him to divide his army into three corps. Umar appointed Habib ibn Muslaima to capture Tiflis, Abdulrehman to march north against the mountains and Hudheifa to march against the southern mountains. With the success of all three missions, the advance into Armenia came to an end with the death of Umar in November 644. By then almost the whole of the South Caucasus was captured.