BAGHDAD — A roadside bomb and three female suicide attackers exploded in quick succession among Shiite pilgrims in Baghdad today, while in the country's north, another suicide bomber attacked a Kurdish protest rally. At least 57 people were killed and 300 wounded.

The attacks were a blow to recent security gains that have seen violence in Iraq drop to its lowest levels in four years.

The violence began in Baghdad, when a roadside bomb and three suicide attackers exploded in quick succession among crowds of Shiite pilgrims marking the death of an eighth-century saint, killing at least 32 people and wounding 102.

A senior U.S. military official blamed al-Qaida in Iraq for the attacks in Baghdad.

A senior U.S. military official blamed al-Qaida in Iraq for the attacks in Baghdad. The attacks come ahead of U.S. and Iraqi military operations in early August aimed at routing out insurgents from rural hideouts in northern Iraq.

In a separate attack, another suicide bomber killed at least 20 people and wounded scores of others at a Kurdish rally in the northern city of Kirkuk, Iraqi authorities said.

The demonstrators were protesting a provincial elections measure blocked in parliament because of disagreement over a power-sharing formula in the disputed city of Kirkuk, an oil-rich area.

ISTANBUL, Turkey — Bomb blasts that killed 17 people and injured 150 others in a crowded neighborhood square appeared to be linked to a Kurdish rebel group, Istanbul's governor said today, though the rebels immediately denied involvement.The attack happened on the eve of a court's deliberations on whether to ban the Islamic-oriented ruling party for allegedly trying to undermine secularism, and the timing raised questions about whether there was a link.Authorities said the vast majority of the 17 deaths and 150 injuries occurred when a curious crowd gathered after an initial, small blast.