The number of girls and women travelling from the UK to Syria is rising after new figures revealed 56 are thought to have fled to the war-torn country last year.
Counter-terrorism officers said they were "deeply concerned" about the number of cases as many women were unaware that they will probably never be able to return home.
Figures released in July showed 43 females were thought to have fled from the UK to Syria in the previous 12 months.
In latest figures, 56 girls and women reported missing by their families between January 1 2015 and December 31 2015 are "all feared to have travelled to Syria", police said.
The figures were disclosed as a short film was released featuring three female Syrian refugees talking about the harsh realities of life in their home country.
The women, named only as Faten, Esaaf, and Zakaa, have also written open letters urging British mothers to take steps to prevent their daughters travelling to the war-zone.
In one letter, Zakaa revealed she left Syria because she feared for the lives of her three sons - including one who has leukaemia - after her husband was killed by a sniper.
"Ask your daughter to think about what she has here in the UK," she wrote. "A country where she has safety and freedom of choice compared to Syria where, under Isis control, she would have neither.
"Isis is far from the views of Islam. They do not follow Islam and they are not Muslims. Isis is more feared by Syrians than the Assad regime itself.
"Isis is not in any way helping Syrians - their only achievements are killing and displacement. They have only damaged our country and caused more harm for innocent Syrian people."
Scotland Yard's Deputy Assistant Commissioner Helen Ball said: "We are deeply concerned about the numbers of girls, young women and also families who are taking the decision to go to Syria, unaware of the dangers they face when they arrive and the fact that they are unlikely to ever be able to return home to their devastated wider families.
"The personal accounts of the women in this film highlight the harsh reality of life for women and children living in a war torn country. I hope they will go some way to helping young women and mothers stop and think about the huge mistake they would be making if they travel."
Recent high profile cases have included school friends Shamima Begum and Amira Abase, both 15, and Kadiza Sultana, 16, all from Bethnal Green, east London, who left for Syria in February. Some are now thought to be married to Isis extremists.
Assistant Chief Constable Angela Williams, of West Yorkshire Police, said: "It is important for everyone do everything they can to help stop people from travelling to Syria and other conflict zones.
"Children have been taken to dangerous places and are at great risk; vulnerable people have been brainwashed into travelling.
"My message to mothers across the region is to please come forward if you have any concerns about your loved ones who may be considering travel to Syria."