Three mortar bombs landed inside Saudi Arabia on Monday close to its northern border with Iraq, where Islamist militants have grabbed land in a lightning advance, officials said.

The mortars caused no casualties but will stoke security fears in Saudi Arabia, which is also facing militants on its southern border with Yemen, where at least 10 people died in an al Qaeda raid into the kingdom on Friday and Saturday.

Authorities in Saudi Arabia, the world’s biggest oil producer, said they were still looking into who fired Monday’s rounds, which landed near a block of flats outside the northern town of Arar. […]