Shops and markets have closed in the Pakistani town of Sheikhopura following an attack on the local Shi'a community which left 12 people dead.

The town's police chief, Ali Amir, said the situation was tense and that there was "an atmosphere of harassment" among the minority Shi'a and majority Sunni Muslims.

The killings took place on Sunday when six men on motorcycles drove into the town and opened fire several times, on one occasion near a Shi'a mosque.

Two policemen were among those killed.

The violence in Sheikhopura followed the execution last week of Nawaz Haq, a leading member of Sunni extremist group Sipah-e-Sahaba Pakistan (SSP), but it is not clear whether there is any connection.

Arrests

No one has claimed responsibility for the attack.

However, one report said the authorities had made a number of arrests, including one man described as a member of a an extremist group called Laskhar-e Jhangvi.

One police official said the man was involved "multiple sectarian murders".

Immediately after the attack, armed Shi'as took to the streets and threatened SSP members.

Several thousand people have died in sectarian violence between the majority Sunni and minority Shi'a communities in the past decade.