BASRA: A string of bomb blasts in predominantly Shia provinces of Iraq killed at least 15 people on Sunday, police and medics said.

The largest explosion took place in the southern oil hub of Basra, where at least eight people were killed when a bomb exploded near the headquarters of a Shia political party.

The violence is part of a sustained campaign of militant attacks since the start of the year that has prompted fears of wider conflict in a country where ethnic Kurds and Shia and Sunni Muslims have yet to find a stable power-sharing compromise.

It was not clear who was behind Saturday's explosions, but Sunni Islamist insurgents, including the al Qaeda-affiliated Islamic State of Iraq, have been regaining strength in recent months, security sources say.

Sectarian tensions have been inflamed by the civil war in neighbouring Syria, which is fast becoming a region-wide proxy war, drawing in Shia and Sunni fighters from Iraq and beyond to fight on opposite sides of the conflict.

On Saturday, two bomb attacks near Sunni mosques in Baghdad killed at least 23 people who had gathered to pray after breaking their daily fast for the Muslim holy month of Ramadan.

More than 300 people have been killed so far in July, according to the violence monitoring group Iraq Body Count.

Fears are growing that Iraq could descent back into all-out civil conflict, although the level of violence is still well below the height of sectarian bloodletting in 2006-07, when the monthly death toll sometimes topped 3,000.