The first Anfal stage was conducted between 23 February and 18 March 1988. It started with artillery and air strikes in the early hours of 23 February 1988. Then, several hours later, there were attacks at the Jafali Valley headquarters of the Patriotic Union of Kurdistan near the Iranian border, and the command centers in Sargallu and Bargallu. There was heavy resistance by the Peshmerga. The battles were conducted in a theater around 1, 154 square kilometres. The villages of Gwezeela, Chalawi, Haladin and Yakhsamar were attacked with poison gas. During mid March, the PUK, in an alliance with Iranian troops and other Kurdish factions, captured Halabja. This led to the poison gas attack on Halabja on 16 March 1988, during which 3,200–5,000 Kurdish people were killed, most of them civilians. The Peshmerga managed to open a flight route to Iran through which a part of the population in the Jafali Valley was able to flee. During the first Anfal campaign, no prisoners were taken by the Iraqi army.