Secretary of State John Kerry called Syria the “world’s strongest magnet for terror” in an unexpected plea for the warring parties there to join peace talks planned for next week.

Kerry directed his call in particular toward a coalition of Syrian opposition groups that plans to to decide Friday whether to attend the Geneva 2 peace talks in Switzerland. Kerry said the U.S. “urges a positive vote” from the group, known as the Syria Opposition Coalition.

The Geneva 2 talks aim to lay the groundwork of a transitional government that, Kerry said, “is the only way to bring about an end to the civil war that has triggered one of the planet’s most severe humanitarian disasters and which has created the seeding grounds for extremism.

On Thursday, the National Coordination Body, an internal opposition group apart from the armed insurgency, said it would not attend the talks, accusing Russia and the U.S. of rushing the conference to serve their own interests, Reuters reports.

Syria’s civil war is nearing its third year and has left more than 100,000 people dead. The region has also become a breeding ground for Islamist militants who have taken up the cause of the Syrian opposition, with Western leaders increasingly concerned that jihadi militants – including people arriving from Europe and the U.S. – could turn their sites on the West.

“The world needs no reminder that Syria has become the magnet for jihadists and extremists,” Kerry said in his statement Thursday. ”It is the strongest magnet for terror of any place today.”