The Islamic State (ISIS) is busy preparing for the mother of all battles against enemy forces in its de-facto capital Raqqa, posting notices around the bomb-ravaged Syrian city that all boys above the age of 14 had to register their names and addresses to the religious police for conscription.

This was revealed by activists who managed to leave the city and flee to southern Turkey, the Daily Express reported.

The activists said the youngsters were given one week to comply with the order or face an unspecified punishment, which most certainly includes execution.

Reports said the ISIS leadership has devised a grand plan to turn the city into a fortress, expecting that its enemies will eventually launch a massive invasion on its capital.

In light of this, the ISIS has issued a stern warning preventing Raqqa residents from leaving so that they could help in resisting the invasion or be used as human shields for ISIS fighters.

Raqqa, the political and military nerve centre of ISIS, has been pounded for days by heavy French and Russian airstrikes. Western military leaders believe its recapture will spell the end of ISIS.

The conscription of youngsters in Raqqa came amid reports that Arab and Kurdish forces, backed by Britain and America, are preparing for an assault on the ISIS stronghold.

ISIS forces in Raqqa have reportedly been hit hard by deaths and defections amid the relentless bombing by Russian and French warplanes.

ISIS terrorists could pose as medical workers to attack hospitals

Meanwhile, Belgian authorities have expressed fears that ISIS terrorists could impersonate fire fighters and medical staff to attack hospitals in Brussels.

Government officials have issued warnings to emergency services that terrorists could slip in undetected by impersonating them, the Daily Express reported.

Accordingly, hospital chiefs have been advised to secure staff uniforms and update their emergency plans and lists of doctors and senior staff.

The new concern was raised after full-body protective suits were stolen from a locked store in a Paris hospital, leading to speculation that ISIS supporters were behind the theft and could use the suits for a chemical or biological attack.