Bomb blasts rock Karachi

An injured boy is taken to hospital after a bomb blast on Wednesday

KARACHI, Pakistan -- Police are probing a spate of bomb blasts that have rocked Pakistan's southern city of Karachi this week, including one that killed a boy.

Two bombs exploded Thursday, killing a 12-year-old boy and wounding six members of his family, in the second straight day of attacks in the restive port city, police said.

On Wednesday, at least 18 people were wounded, some of them critically, after two bombs went off within 10 minutes of each other in a different section of the city, police said.

No one has claimed responsibility for the blasts. Police described them as a ploy to create terror in the city where a one-day strike was called for Thursday to protest the killings of two prominent members of the United National Movement last week.

The Muttahida Qaumi Movement (MQM) called for the strike throughout Sindh province, angry at the government for failing to track down the killers.

The MQM speaks for the political and economic rights of Muslims and their descendants who migrated to Pakistan during the partition of the subcontinent in 1947.

Police have in the past blamed the MQM for most of the bloodletting in Karachi, including the killing of its political rivals.

The movement denies the charge and accuses the authorities of targeting its members and supporters. Police reject the movement's allegation.

The explosions underline the challenges facing Pakistan President Pervez Musharraf as he tries to curb violence and extremism in the poor South Asian Islamic nation.

Thursday blasts

A plainclothes policeman investigates the site of a Wednesday blast

The first bomb Thursday exploded about 3 a.m. (2100 GMT Wednesday) in the low-income Lines Area neighborhood.

The boy who was killed and his family were Afghans, Deputy Superintendent of Police Ali Raza told The Associated Press news agency.

The bomb was placed outside their home while they were asleep, he said. There were no immediate details about what type of bomb it was.

The second bomb exploded about two hours later in a market of the affluent Defense Housing Authority neighborhood, damaging two cars and several shops but causing no casualties, police said. The market was closed at the time.

The MQM has denied responsibility for the blasts.

The Pakistani army has been deployed to the city and is patrolling parts of it, including the neighborhood of north Nazimabad, which is a Muttahida Qaumi stronghold.

-- CNN's Ash-har Quraishi and Basma Babar-Quraishi contributed to this report