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(CNN) -- A series of bombings on Turkey's Mediterranean coast and in the commercial center of Istanbul has left 27 people wounded, including 10 British tourists, officials report.

At least three explosions late Sunday left 21 people wounded in the popular coastal resort town of Marmaris in southwest Turkey, CNN Turk reported.

Meanwhile, six people were wounded in Istanbul, three of them seriously, the network reported, citing local authorities and witnesses.

Police sources told CNN Turk the blasts were the result of bombs. There was no immediate claim of responsibility for the attacks.

In London, the Foreign Office said 10 British citizens were hurt in the blasts, and four of them were in serious condition.

Doctors at Caria Hospital in Marmaris treated four Britons and one Turk after a bomb went off on a local minibus, said operations manager Sozanne Poraz.

None of those treated at her hospital had life-threatening injuries. Most suffered cuts and burns on their legs and had difficulty hearing, Poraz said. Two had to have shrapnel removed from their legs.

Most of those treated at her hospital were in shock and unable to provide much of a description of the blast, Poraz added.

One woman "said she was sitting in the back of the bus, heard a large bang and saw an explosion in front of her, but that's all she's been able to tell us," Poraz said.

Julie Midgmey, a spokeswoman for the Ahuhetman Hospital, said four Turks and six Britons were treated there.

Midgmey said "a couple" of people had to have shrapnel removed from their legs, but other wounds were spread across their bodies.

Hospital sources said nine of those who were admitted to hospitals in Marmaris were discharged -- both Britons and Turks