BEIRUT (REUTERS) - Islamic State in Iraq and Syria (ISIS) militants have ordered shopkeepers to shut down their wireless Internet during prayer times in the eastern Syrian city of Deir al-Zor, a group monitoring the Syrian conflict said on Thursday.

It was a further example of ISIS imposing controls on public life as it seeks to build what it describes as a caliphate in the heart of the Middle East.

The ultra-radical insurgents hold large tracts of territory in Syria and Iraq and are the target of a US-led bombing campaign in both countries.

The Britain-based Syrian Observatory for Human Rights cited an Islamic State document obtained by activists which said: "All shopkeepers must stop broadcasting wireless Internet during prayer times."

Muslim prayers are performed five times a day.

The document was issued by the self-declared authorities of Islamic State in the city that control public behaviour, according to the Observatory, which tracks the war using a network of sources on the ground.

ISIS controls most of Deir al-Zor province as well as Raqqa province to the north-west.

In Raqqa, it has outlawed music and images of people being posted in public and runs nearly everything from bakeries to schools, courts and mosques.

The Observatory reported on Sunday that Islamic State in Deir al-Zor had already ordered cafe owners to shut down their Internet overnight to prevent details of its military movements being communicated.

Internet coverage is already patchy in contested parts of Syria, now in its fourth year of civil war.