Insurgents determined to derail this weekend's historic referendum bombed an office of Iraq's largest Sunni Arab political party on Friday, police said, after the group dropped its opposition to the draft constitution. No one was wounded by the roadside bomb just outside the Iraqi Islamic Party office in Fadhal, a district of central Baghdad. But the rare attack against the group by Sunni-led insurgents appeared aimed at punishing it for deciding to end its "no" campaign against the referendum after lawmakers agreed Wednesday night to several amendments to the constitution designed to win Sunni support in Saturday's vote. On Thursday, Iraqi Islamic Party banners urging a "no" vote had been removed from where they hung near monuments such as the capital's main Grand Imam mosque. "This attack by insurgents against the Islamic Party was expected because of its new stand toward the referendum," Iraqi army Maj. Salman Abdul Yahid said in an interview. "Insurgents had threatened to attack the group and its leaders to get revenge."