On 6 October 1973, in a surprise joint attack, Egypt attacked Israeli forces on the Suez Canal and in the Sinai while Syria attacked Israeli forces on the Golan Heights. Israel eventually repulsed the Syrian operation, and crossed the Suez Canal through a gap between Egyptian forces. Israeli forces then pushed further into Syria, and encircled elements of the Egyptian 3rd Army. Fighting continued until 22 October 1973, when United Nations Security Council Resolution 338 called for a ceasefire. The next day the ceasefire was violated and fighting resumed, resulting in United Nations Security Council Resolution 339. Resolution 339 primarily reaffirmed the terms outlined in Resolution 338 (itself based on Resolution 242). It required the forces of both sides to return to the position they held when the initial ceasefire came into effect, and requested the United Nations Secretary-General to undertake measures toward the placement of observers to supervise the ceasefire.