Fifteen people were killed overnight Thursday in separate attacks by insurgents in Iraq's northern province of Nineveh, security sources said. The deadliest attack occurred late Wednesday when dozens of gunmen attacked an army base in al-Mahallabiyah area in west of the provincial capital city of Mosul, some 400 km north of Baghdad, an army source told Xinhua on condition of anonymity. The attackers came riding more than 20 vehicles and fought a fierce clash with the soldiers for three hours, the source said. The battle caused 13 killed including five soldiers and five others wounded, the source added. In a separate incident, a soldier was killed and another wounded when a roadside bomb struck their foot patrol in eastern Mosul, a provincial police source told Xinhua on condition of anonymity. Also in Mosul, gunmen broke into a shop and shot dead the owner from Shabak minority, the source said. Shabak people are a Shiite minority group living in Iraq's northern province of Nineveh, particularly around Mosul. The violence came less than two weeks ahead of landmark parliamentary elections on April 30, the first in the country since the withdrawal of U.S. troops in late 2011.