One rocket was fired from the Gaza Strip at the southern city of Ashkelon on Sunday evening, the Israel Defense Forces confirmed.
The rocket struck in an open area, causing no injuries or damages, according to the military.
The Iron Dome air defense system was not activated as the projectile was not headed for a populated area.
Palestinian terror groups said the launch was the result of a technical malfunction.
In response, the IDF struck a Hamas observation post in Gaza.
Israel and the Gaza-based Palestinian Islamic Jihad on Saturday night reached a ceasefire agreement to end five days of conflict.
Israeli media reported that the defense establishment did not expect the latest rocket attack to reignite the fighting.
While Hamas did not participate directly in the hostilities, Jerusalem has a longstanding policy of holding Gaza’s rulers responsible for attacks emanating from the enclave.
During “Operation Shield and Arrow,” PIJ fired 1,469 projectiles at Israel, of which 1,139 crossed into the Jewish state (there were also 291 failed launches, or 20% of all PIJ rockets).
Iron Dome intercepted more than 95% of rockets heading for built-up areas. David’s Sling intercepted two rockets, making its operational debut. The IDF struck more than 371 PIJ targets, including command and control apartments, usually located in one- to three-story residential buildings, which the IDF warned so they could be evacuated before it attacked them.
The strikes on military leaders and command and control centers placed PIJ under pressure, ultimately pushing its Beirut-based leader Ziyad al-Nakhalah to accept a truce.