A string of explosions wounded at least 37 people Monday in the southern Pakistani city of Karachi, rattling the country a day after a deadly suicide attack in the capital, police said.

The six blasts came within about an hour of each other, striking residential and commercial spots in the teeming port city, where political and militant-related violence is common.

Television footage showed ambulances rushing people through Karachi's crowded streets to hospitals and victims lying in hospital beds with bloody bandages.

There was no immediate claim of responsibility, just as there has not been for the Sunday blast in Islamabad, which left at least 18 people dead, most of them police officers.

Babar Khattak, Sindh province police chief, said that it appeared that 150-200 grams of explosives were used in each of the six Karachi blasts — only enough to create a relatively small blast.

"It seems the series of blasts was carried out to create harassment and fear among the citizens," Khattak said. He also noted that the areas struck had large Pashtun populations and said the explosions may have been aimed at creating ethnic unrest.

Interior Ministry chief Rehman Malik said the blasts appeared to have been pre-planned and aimed at destabilizing the city.

It was not clear how many of the 37 wounded were civilians or how badly they were injured.

Two of the bombs were apparently planted in a taxi stand and a pickup truck full of scrap, according to Wasim Ahmed, Karachi's police chief.

Karachi is Pakistan's main port and commercial hub. In October, former Prime Minister Benazir Bhutto narrowly escaped a suicide attack there that struck a rally of thousands of supporters welcoming her home from exile.

More than 140 people were killed in that attack. Bhutto was later slain in a separate attack in December in Rawalpindi.

Khattak said security forces had intensified patrols in the affected Karachi areas Monday.