British police fear two teenage boys who recently vanished from their homes have entered Islamic State-controlled territory in Syria.
Authorities said Tuesday that they were "deeply concerned" for the welfare of the pair, who have not been seen since March 31 and would be the latest in a growing list of young Britons to travel to the Middle East to join the militants.
One of the teens is believed to be the brother of Britain's youngest convicted terrorist, Hammaad Munshi, who was 15 when he was arrested on his way home from school by counter-terrorism police in 2006. He had downloaded instructions for how to make napalm and was convicted under the Terrorism Act in 2008 for being part of a plot to kill non-Muslims.
The missing boys were widely named by British news media as Hassan Munshi and his close friend Talha Asmal, both 17, who lived close to each other in the northern English town of Dewsbury. Police would not confirm or deny the reports.
Hassan Munshi's grandfather is a well-respected Islamic scholar, Yakub Munshi, who spearheaded the creation of the town's first sharia, or Islamic law, court and is head of the local mosque.
Police said the boys took advantage of spring break to slip out of the country on a flight from Manchester to the Turkish city of Dalaman, where they are thought to have crossed the border by land to Syria. They told their families they were going on a school trip, but alarm bells were raised when they did not respond to calls and messages on their cellphones.
"Our priority is for their safe return; their families are gravely worried about them and want them home," Assistant Chief Constable Mark Milsom of West Yorkshire police said. "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," he said.
British authorities believe as many as 600 Britons have traveled to Syria or Iraq to fight alongside the militants, and are increasingly worried about the number of young people being radicalized.
In recent weeks, Turkish authorities have thwarted several attempts by Britons to cross the border, including a group of three men, two women and four children.
The last known successful attempt by British nationals to cross into Syria was made by three East London schoolgirls, Shamima Begum, Amira Abase and Kadiza Sultana, who flew to Turkey in February and were then smuggled into Syria. They were believed to be following a fourth girl from their school in Bethnal Green who made the journey in December.
Turkish authorities have been criticized for failing to secure the southeastern border with Syria but have in turn hit back at European nations for failing to stop people leaving and failing to give Turkish security services ample time to act.