A bomb exploded near a Shiite religious procession in northwest Pakistan on Saturday killing seven people including four children, hospital officials said.

At least 30 people including five other children were also wounded when the remote controlled bomb packed with ball bearings exploded on the outskirts of Dera Ismail Khan city in Khyber Pakhtunkhwa province.

The blast went off as people from the minority Shiite Muslim community were gathering to mark the anniversary of the death of the Prophet Mohammed's grandson Imam Hussain in 680.

Security was tight across the country to prevent such attacks on Shiite commemorations. Pakistan on Friday suspended mobile phone services in major cities -- mobiles are often used to trigger bombs.

"The death toll is now seven, four of them are children," local hospital chief Aziz Baluch told AFP. "Four of the wounded were in critical condition, they have been shifted to the central city of Multan."

Akhtar Nawaz, another official at the state run District Headquarters Hospital said three children were already dead on arrival, while four other people died in hospital.

The 10 kilogram remote controlled device carrying ball bearings was planted on the route of a religious procession of the minority Shiite community, police officer Ghulam Ahmed told AFP.

"The bomb was planted in a dustbin, the blast was powerful and heard several kilometres away," another police official Siddiq Khan said.

City police chief Khalid Suhail said the dead children were aged between six and 11 years. "They were young boys," he said.

Mobile and wireless phone services were temporarily blocked in the commercial capital Karachi, the southwestern city of Quetta and several cities and towns in northwestern Khyber Pakhtunkhwa and central Punjab provinces as well as in parts of the capital Islamabad.

It is the second time Pakistan has shut down mobile networks during the holy month of Muharram, which culminates with Ashura, the holiest day in the Shiite Muslim calendar when the faithful march to mourn the death of Imam Hussein.

Authorities beefed up security across the country amid intelligence reports of possible attacks on Shiite gatherings.

A suicide bomber killed 23 people and wounded 62 others at a Shiite procession in Rawalpindi on Thursday, the deadliest bombing in Pakistan for five months.

Ashura falls this year on Sunday and has been a magnet for sectarian attacks with rights groups heavily criticising the government for failing to stop extremist violence.

In December 2009, a suicide bomber killed 43 people in Karachi at a Shiite procession to mark Ashura.

Shiites account for around 20 percent of Sunni-dominated Pakistan's 167 million population.

Nationwide sectarian violence between militants from the two communities is estimated to have killed more than 4,000 people since the late 1990s.

Pakistan says 35,000 people have been killed as a result of terrorism since the 9/11 attacks and the 2001 US-led invasion of neighbouring Afghanistan.