The Iraqi government offered up a rare bit of good news, announcing it had liberated Eastern Mosul from the Islamic State, after months of deadly street-to-street fighting.

Iraqi forces dislodged the final remnants of Islamic State militants from their strongholds in the eastern part of Mosul, Iraq’s second largest city. It’s a major milestone for the Iraqi government, which has been fighting to regain control from the Islamic State, which first took Mosul in the summer of 2014. As security forces rolled back the Islamic State, thousands of families reentered Eastern Mousl to rebuild their lives.

“This is a monumental achievement for not only the Iraqi security forces and sovereign government of Iraq, but all Iraqi people,” Lt. Gen. Stephen J. Townsend, the general commanding anti-Islamic State coalition forces in Iraq, said in a statement released on Tuesday. In a public address to the nation on Tuesday, Iraqi Prime Minister Haider al-Abadi praised the “unmatched heroism of all security forces.”

But the fight’s not over; it now shifts to Western Mosul, across the Tigris River. Though Iraqi military leaders say its security forces have already killed most Islamic State commanders in Mosul, its security forces may face an even fiercer battle when it pushes west. “There is still a long way to go before IS is completely eliminated from Iraq, and the fight for Western Mosul is likely to be even tougher than the Eastern side,” said Townsend.

An estimated 750,000 people still reside in Western Mosul under ISIS rule, which could further complicate the fight. Rights groups have already raised the alarm on the number of civilians at risk.