Saudi Arabia says it has intensified airstrikes against the Shiite rebel stronghold in Yemen in response to cross-border attacks targeting Saudi cities.

The Saudi Press Agency said Friday that coalition airstrikes targeted the northern province of Saada — which is the stronghold of Shiite rebels known as Houthis — destroying a land-mine factory, a telecommunications complex and command centers.

The Houthis have overrun the Yemeni capital and are allied with forces loyal to ousted President Ali Abdullah Saleh. They are currently engaged in an offensive in southern Yemen.

The rebels fired rockets and mortars into Saudi Arabia on Tuesday, killing at least three people.

The coalition's spokesman, Saudi Brig. Gen. Ahmed Asiri, vowed a "harsh response" and said the Houthis "made a mistake by targeting Saudi cities."