If they seize the provincial capital, Baquba, ISIS will be able to attack Baghdad from three directions.

Via CNN:

On Sunday, the militant group continued its assault. Iraqi security forces and gunmen believed to be ISIS clashed near al-Khalis, which is about 18 miles from Baquba, police officials in that Iraqi city told CNN.

Baquba is about 37 miles northeast of Baghdad, the capital. ISIS seized Iraq’s second-largest city, Mosul, last week and have threatened to march on Baghdad.

Also Sunday, ISIS gained control of two villages in Adhaim, a move that constituted the militants’ first push into Diyala province, which is northeast of Baghdad.

Baquba, Diyala’s capital, is an ethnically-mixed city, though Sunnis represent a slight majority.

Given Baquba’s proximity to Baghdad, if Baquba were to fall, it could give ISIS militants three-pronged access to Baghdad — from Anbar province to the west, Ninevah and Salahuddin provinces to the north and from Diyala province from the northeast.