India's home minister says authorities believe the back-to-back blasts that killed at least 13 people in Mumbai were a “coordinated attack by terrorists.”

P. Chidambaram appealed for calm, after three separate explosions struck India's financial capital Wednesday evening. The home minister said more than 54 people were wounded, and authorities expect the number of casualties to rise.

Police say two of the blasts occurred in the south of the city, near the popular Opera House and famed jewelry market Zaveri Bazaar. The other blast hit the crowded Dadar neighborhood in the center of the city.

Mumbai's police commissioner, Arup Patnaik, told reporters that bomb disposal squads have been deployed. He said a preliminary investigation found that an improvised explosive device was placed in an umbrella at one of the scenes. He refused to comment on whether authorities had intelligence suggesting a terrorist attack was imminent.

So far, no one has claimed responsibility for the blasts.

Local television showed chaotic scenes with debris scattered at one explosion site and medical teams treating the injured elsewhere.

Mumbai is no stranger to attacks. In 2008, Pakistan-based militants laid siege to the city, killing 166 people. Domestic militant groups also are active in the country and have carried attacks in large cities.