Train service was suspended in Pakistan after a series of blasts Saturday blew up railway tracks near the port city of Karachi and several other cities of southern Sindh province, said railway officials.

No one was hurt in the blasts, they said.

A senior railway official Zafarullah Kalur said that four blasts damaged nearly four-foot tracks in Sindh province, of which Karachi is the capital.

Local TV channels reported 12 small blasts at different places early on Saturday in Sindh province, including Karachi, Hyderabad, Sukkar, Nawabshah, Khairpur and Mirpur Mathilo.

TV footage showed damaged parts of the tracks.

Kalur said that trains were stopped after information was received and teams were immediately sent to repair the damaged tracks.

No group claimed responsibility for the blasts.

A little known group "Sindh Liberation Army" had claimed responsibility for similar blasts in the past. Officials said they do not have any clues so far as to who are behind the blasts.

Kalur said small blasts on tracks have been occurring for two years.

He said tracks would be repaired and train service restored in a couple of hours. He said trains were stopped at different places.

General Manger Railways Saeed Akhtar described the blasts as terrorist acts and said that security for the tracks has been furthered tightened after the blasts.

He said coordination with provincial authorities will be improved to step up patrolling on tracks to avoid such incidents in future.

Civil and railways police arrived at blast sites and also registered cases against the unidentified suspects.

Sources said it is the second time in the country that the tracks have been targeted this year.