ISLAMABAD, PAKISTAN: A bomb exploded on a crowded bus, killing at least 40 people heading home for Eid al-Adha,Islam's most holy day. At least 26 others were injured in the blast, some seriously. No group has yet taken responsibility, says TIME's Ghulam Hasnain, but groups opposed to Prime Minister Benazir Bhutto's government are likely behind the incident. Sunday's blast follows a string of passenger bus explosions in Lahore during the last year. Many of these acts have been attributed to internal sectarian rivalry, says Hasnain: "In last few months, there has been a gradual increase of pressure on Bhutto's government. Militant groups opposed to Bhutto choose to target passenger busses because they can then say her government has failed to maintain law and order."