A roadside bomb exploded on Wednesday near a bus carrying Iranian pilgrims to Iraq's holy Shia shrine city of Karbala, wounding seven of them, security officials said. The blast came a day after Iraqis celebrated the beginning of Muharram, the first month of the Islamic calendar, and as Shias from around the world descend on Karbala for the commemoration of Ashura, which marks the slaying of the revered Imam Hussein by the armies of the Sunni caliph Yazid in 680.

It struck the bus in southwest Baghdad while it was en-route to Karbala at about 7:30am (0430 GMT), leaving seven Iranians wounded, officials from the interior and defence ministries said on condition of anonymity.

The bombing followed two separate attacks in the capital on Saturday that also targeted Iranian pilgrims visiting Shia holy sites in Iraq, killing six religious tourists.
Every day, thousands of pilgrims, many of them from Iran and other countries with large Shia Muslim populations, visit Karbala and Iraq's other major Shia shrines in Samarra, Najaf and Baghdad.

That number rises dramatically during the first 10 days of Muharram, known as Ashura, as millions of pilgrims travel to Karbala, the home of shrines to Imam Hussein and his half-brother Imam Abbas, culminating on the 10th day of the month, according to the lunar calendar.

While the government in Baghdad declared a national holiday on Tuesday for Muharram, Iraq's top Shiite cleric Grand Ayatollah Ali al-Sistani has said Muharram began on Wednesday, meaning Ashura is to climax on 17 December.

Shia make up about 15 per cent of Muslims worldwide. They represent the majority populations in Iraq, Iran and Bahrain and form significant communities in Afghanistan, Lebanon, Pakistan and Saudi Arabia.

In a separate attack on Wednesday in the town of Taji, 25 kilometres (15 miles), one person was killed and 17 others wounded when a car bomb detonated at about 10am (0700 GMT), an interior ministry official said.

The blast, which occurred near a popular restaurant in the town, had targeted an Iraqi army patrol, but no soldiers were among the casualties.

While violence has dropped dramatically across Iraq since its peak in 2006 and 2007, attacks remain common, especially in Baghdad and the restive northern city of Mosul. The number of people killed in violence in Iraq last month was the lowest in a year for the second month running, with 171 people -- 105 civilians, 23 soldiers and 43 policemen -- dying in attacks.