A customer, three station attendants and a security guard were lightly wounded in the attacks, which began at dawn, said Shell Pakistan.

File pictureof Karachi following a
spate of violence

There was no serious damage to any of the stations.

Small devices packed into boxes were placed inside garbage bins at the stations. The attacks were aimed to cause panic, said Deputy Inspector General of Police Tariq Jamil.

“The target was Shell,” said Jamil.

Pakistan’s main commercial city has seen a series of attacks against Western targets.  Police have rounded up suspects in recent months.

Shell said it was “shocked and concerned” by the attacks and took steps to tighten security at all its facilities in Pakistan.

Security was also stepped up at all foreign business interests in Karachi, said Jamil.

Shell Pakistan is one of Islamabad's biggest foreign-investment firms.

Past attacks in Karachi have been blamed on groups opposing Islamabad’s decision to back Washington’s “war on terror”, launched after the 11 September attacks.