On September 15, King Hussein declared martial law. The next day, Jordanian tanks (the 60th Armored Brigade of the Jordanian Army) attacked the headquarters of Palestinian organizations in Amman; the army also attacked camps in Irbid, Salt, Sweileh, Baq'aa, Wehdat and Zarqa. Then the head of Pakistani training mission to Jordan, Brigadier Muhammad Zia-ul-Haq (later Chief of Army Staff and President of Pakistan), took command of the 2nd division.[12][13] However the Jordanians could not devote all their attention to the Palestinians. The 3rd Armoured Division of the Iraqi Army had remained in Jordan after the 1967 war. The Iraqi regime sympathised with the Palestinians, and it was unclear whether the division would intervene on the part of the Palestinians. Thus the 99th Brigade of the Jordanian 3rd Armoured Division had to be retained to watch the Iraqi division.[14]

Arafat later claimed that the Jordanian army killed between 10,000 and 25,000 Palestinians, although more conservative estimates put the number between 1000 and 2000.[15][16]