Pakistani police and paramilitary forces were on high alert Tuesday after a bomb killed 10 people in this teeming port city in a bid to derail key February elections, officials said.
The bombing coincided with a visit to Karachi by President Pervez Musharraf and officials said it was intended to sow fear ahead of February 18 polls, already delayed once by the assassination of opposition leader Benazir Bhutto.
Bhutto's widower, Asif Ali Zardari, was also in the city of 12 million people but there was no suggestion either man was targeted.
"Police have been put on red alert and they will be assisted by Rangers (paramilitary forces)," Karachi police chief Azhar Farooqi said.
He said security forces were conducting random spot-checks on commuters and vehicles at all entry and exit points to the city, Pakistan's largest.
Paramilitary Rangers spokesman Captain Mohammad Fazal said troops were fanning out across the city.
"We have deployed 10,000 personnel at all sensitive points and installations," he said, adding that another 4,000 were on standby.
"The situation in under control and we are on the highest alert."
The blast ripped through a crowded street market outside a factory Monday evening, the latest in a spate of dozens of bombings which have rocked the nuclear-armed US ally over the past 12 month, claiming more than 800 lives.
"There was no specific target, it was just meant to kill ordinary civilians. The terrorists chose a soft target to spread panic and terrorise society," interior ministry spokesman Brigadier Javed Cheema said.
Officials said the bloodshed was meant to force the government to push back the elections again, a move that would further damage its credibility in the eyes of the people who are desperate for a return to full democracy.
Ex-general Musharraf took power in a military coup in 1999 but has come under mounting criticism for failing to stem the growth of Islamic militancy sparked by the US-led "war on terror" in neighbouring Afghanistan.