BAGHDAD  A bombing on Monday evening killed 43 people near the Imam Hussein shrine in the Shiite holy city of Karbala, penetrating one of the most secure perimeters in Iraq. Iraqi police officers at the scene and several witnesses said it had been carried out by a female suicide bomber, but the police chief later said the bomb had been hidden.

The explosion, the deadliest attack in Karbala in nearly a year, overshadowed a Baghdad visit by Vice President Dick Cheney, who met with Iraqi and American leaders and extolled what he described as “phenomenal” security improvements in the country.

Arriving on the eve of the five-year anniversary of the war, the vice president strove to label the invasion and occupation a success. “If you reflect back on those five years, I think it’s been a difficult, challenging, but nonetheless successful endeavor,” he said in Baghdad, adding that “it’s been well worth the effort.”

The explosion rocked central Karbala about 6 p.m. “Many people were killed and wounded,” said Abu Ahmed, 36, who minutes earlier had walked past the site and then came rushing back to help the wounded. “Everyone near the bomber was killed.”