The Islamic State group has claimed the killing of four members of Pakistani security forces who were shot dead by gunmen on a motorcycle in the southwestern city of Quetta.

The statement issued Sunday gave no further details about the attack, which took place the day before.

The IS affiliate in Pakistan has grown in recent months by attracting disgruntled Taliban militants and by partnering with a violent sectarian group that targets the country's Shiite minority. IS claimed an attack on a Sufi shrine earlier this month that killed more than 50 people.

Pakistan has stepped up security ahead of Shiite processions on Sunday and Monday to mourn Imam Hussein, the slain grandson of Prophet Muhammad.