However, while the Christian states did not make any attempt to exploit the victory, the Turks' reaction was swift. In 1388 a 30,000 strong army commanded by Ali Pasha passed through the eastern Balkan Mountains and struck deep into Bulgaria's north. The Bulgarians were completely surprised and the invaders seized Ovech, Shumen, Madara and other towns. Due to the surprise campaign at first the towns and the castles were unable to organize proper defence but after the initial shock the Bulgarians took precautions. When the army of Ali Pasha besieged Varna, the defenders stiffly resisted and the Turks were forced to abandon the siege and march northwards.