Shia in Iraq have come under frequent attack by Wahhabi terrorists of ISIS who regard them as heretics and who still control some territory in Anbar province, to the west of Karbala, though attacks in the city itself are rare.
Imam Hussein, the grandson of the Prophet Mohammed, is buried in Karbala, and Shia pilgrims pack the city each year for Ashura commemorations, which mark his martyrdom in the 7th century.
"Our forces from the army and local and federal police took strict security measures culminating today to protect pilgrims in and around Karbala," police spokesman Colonel Alaa al-Ghanimi said.
"Forces from the Hashed al-Shaabi have implemented security measures to control areas in the west of Karbala province," Ghanimi said, referring to an umbrella organization for pro-government militiamen.
According to Ghanimi, some 30,000 security personnel are taking part in efforts to guard the city and its surroundings.
On Tuesday, pilgrims sang songs about the story of Imam Hussein's martyrdom.
Black banners were draped around the city, and pilgrims, most of them black-clad, packed the streets around the shrines of Imam Hussein and his brother Abbas.
The number of pilgrims participating in the Ashura commemorations is expected to be huge, with Karbala deputy governor Ali al-Mayali saying it was expected to reach three million.
Some 250,000 pilgrims have arrived over the past two days, Mayali said.
Ghanimi said there had been no security breaches so far, and while ISIS frequently targets Shia in Baghdad and elsewhere, Karbala is usually much more secure.
