Major-General Raed Shakir Jawdat, Karbala's police chief, said 40,000 personnel, including more than 2,000 women police workers, were involved in security.
Jawdat said the pilgrimage was a success despite the deaths of 36 pilgrims killed since Thursday. He said security would continue until the pilgrims had left the city.
"The pilgrims were aware that these measures were for their safety and to protect them from terrorist attacks," he said.
Jawad Bolani, the Iraqi interior minister, said the security forces had been
"controlling" the province for the past two weeks.
"There was collaboration between Baghdad police and neighbouring provinces of Karbala. There were special forces from the ministry of interior who also took part."
Ehsaan al-Asadi, one pilgrim from the southern city of Nasiriyah, praised the operation.
"This was the most successful ceremony since the fall of the [Saddam Hussein] regime because we did not face any problems as we marched for seven days to reach Karbala."
|Iraq's interior minister said pilgrims were attacked by al-Qaeda [AFP]
Mohammed Abdallah, a Shia from the northern town of Tal Afar, said he was not scared.
"I had no fear. This year the pilgrimage was successful."
Last year, gunfights in Karbala killed at least 52 people.
The unrest was blamed on the al-Mahdi Army, a militia run by Muqtada al-Sadr.
On Saturday, at least six people were killed in a car bombing in Baghdad targeting the pilgrims.
The worst attack was on Thursday when two women suicide bombers detonated their vests in Iskandariyah, south of Baghdad. They killed 22 people and wounded at least 73, most of them young men.
Bolani said the Iskandiriyah attack was carried out by al-Qaeda.
"The bombing was a desperate measure by al-Qaeda," he said. "The day will come soon when we will announce that al-Qaeda's coffin has been thrown in the garbage of history."