BAGHDAD (Reuters) - Islamic State stepped up attacks on Iraqi army positions near the border with Syria, killing seven soldiers and wounding 12 in two attacks staged on Sunday and Tuesday, military sources said.

Islamic State has been fighting since October a U.S.-backed offensive in Mosul, the largest city that fell under its control in both Syria and Iraq.

Four soldiers were killed and four wounded on Tuesday in an army position near Rutba, a town that controls the access to both the Syrian and Jordanian borders, the sources said.

Three soldiers were killed and eight wounded on Sunday in Akkashat, north of Rutba, near the Syrian border, they said. Islamic State has already claimed the attack on Akkashat.

The border area with Syria is an historic hotbed of the hardline Sunni insurgency sparked by 2003’s U.S.-led invasion of Iraq, which empowered the oil-rich nation’s Shi’ite majority.

Islamic State, the latest embodiment of this insurgency, overran a third of Iraq in 2014, declaring from the northern city of Mosul a “caliphate” that also spanned parts of Syria.

The militants have been dislodged from most cities they had captured and are now besieged in a northwestern corner of Mosul.