Two British teenage boys from Yorkshire are believed to have travelled to Syria, counter-terrorism police have confirmed.
The 17-year-olds are thought to have fled to the war-torn country after boarding a flight from Manchester airport to Dalaman in Turkey on March 31, West Yorkshire Police said.
Assistant Chief Constable Mark Milsom said: "We are extremely concerned for the safety of these two boys and would urge anyone with information to come forward and speak to us.
"Syria is an extremely dangerous place and the public will be aware of the dangers these boys may face.
"The choice of returning home from Syria is often taken away from those that come under the control of Islamic State, leaving their families in the UK devastated and with very few options to secure their safe return."
Meanwhile, the UN has warned again of the terrible plight of refugees in the war-torn country as President Bashar al-Assad's forces continue to launch strikes and Isil battles to strengthen its hold on large tranches of the country.
The UN has decried the "inhumane" conditions for refugees in Syria.