In Slavonia, the first armed conflicts were clashes in Pakrac, and Borovo Selo near Vukovar. Western Slavonia was occupied in August 1991, following an advance by the Yugoslav forces north from Banja Luka across the Sava River. This was partially pushed back by the Croatian Army in operations named Otkos 10, and Orkan 91, which established a front line around Okučani and south of Pakrac that would hold virtually unchanged for more than three years until Operation Flash in May 1995. Armed conflict in the eastern Slavonia, culminating in the Battle of Vukovar and a subsequent massacre, also included heavy fighting and the successful defence of Osijek and Vinkovci. The front line stabilized and a ceasefire was agreed to on 2 January 1992, coming into force the next day. After the ceasefire, United Nations Protection Force was deployed to the occupied areas, but intermittent artillery and rocket attacks, launched from Serb-held areas of Bosnia, continued in several areas of Slavonia, especially in Slavonski Brod and Županja. The war effectively ended in 1995 with Croatia achieving a decisive victory over the RSK in August 1995. The remaining occupied areas—eastern Slavonia—were restored to Croatia pursuant to the Erdut Agreement of November 1995, with the process concluded in mid-January 1998.