Iran–Iraq War
Operation Mersad and end of the war

Operation Mersad (مرصاد "ambush") was the last big military operation of the war. Both Iran and Iraq had accepted Resolution 598, but despite the ceasefire, after seeing Iraqi victories in the previous months, Mujahadeen-e-Khalq (MEK) decided to launch an attack of its own and wished to advance all the way to Tehran. Saddam and the Iraqi high command decided on a two-pronged offensive across the border into central Iran and Iranian Kurdistan. Shortly after Iran accepted the ceasefire, the MEK army began its offensive, attacking into Ilam province under cover of Iraqi air power. In the north, Iraq also launched an attack into Iraqi Kurdistan, which was blunted by the Iranians.

On 26 July 1988, the MEK started their campaign in central Iran, Operation Forough Javidan (Eternal Light), with the support of the Iraqi army. The Iranians had withdrawn their remaining soldiers to Khuzestan in fear of a new Iraqi invasion attempt, allowing the Mujahedeen to advance rapidly towards Kermanshah, seizing Qasr-e Shirin, Sarpol-e Zahab, Kerend-e Gharb, and Islamabad-e-Gharb. The MEK expected the Iranian population to rise up and support their advance; the uprising never materialised but they reached 145 km (90 mi) deep into Iran. In response, the Iranian military launched its counter-attack, Operation Mersad, under Lieutenant General Ali Sayyad Shirazi. Iranian paratroopers landed behind the MEK lines while the Iranian Air Force and helicopters launched an air attack, destroying much of the enemy columns. The Iranians defeated the MEK in the city of Kerend-e Gharb on 29 July 1988. On 31 July, Iran drove the MEK out of Qasr-e-Shirin and Sarpol Zahab, though MEK claimed to have "voluntarily withdrawn" from the towns. Iran estimated that 4,500 MEK were killed, while 400 Iranian soldiers died.

The last notable combat actions of the war took place on 3 August 1988, in the Persian Gulf when the Iranian navy fired on a freighter and Iraq launched chemical attacks on Iranian civilians, killing an unknown number of them and wounding 2,300. Iraq came under international pressure to curtail further offensives. Resolution 598 became effective on 8 August 1988, ending all combat operations between the two countries. By 20 August 1988, peace with Iran was restored. UN peacekeepers belonging to the UNIIMOG mission took the field, remaining on the Iran–Iraq border until 1991. The majority of Western analysts believe that the war had no winners while some believed that Iraq emerged as the victor of the war, based on Iraq's overwhelming successes between April and July 1988. While the war was now over, Iraq spent the rest of August and early September clearing the Kurdish resistance. Using 60,000 troops along with helicopter gunships, chemical weapons (poison gas), and mass executions, Iraq hit 15 villages, killing rebels and civilians, and forced tens of thousands of Kurds to relocate to settlements. Many Kurdish civilians fled to Iran. By 3 September 1988, the anti-Kurd campaign ended, and all resistance had been crushed. 400 Iraqi soldiers and 50,000–100,000 Kurdish civilians and soldiers had been killed.

At the war's conclusion, it took several weeks for the Armed Forces of the Islamic Republic of Iran to evacuate Iraqi territory to honor pre-war international borders set by the 1975 Algiers Agreement. The last prisoners of war were exchanged in 2003.

The Security Council did not identify Iraq as the aggressor of the war until 11 December 1991, some 11 years after Iraq invaded Iran and 16 months following Iraq's invasion of Kuwait.
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