Spain’s capital is hosting United Nations-backed international talks on the ways to stop extremists joining terrorist groups abroad.

More than 200 experts from 70 countries and about 30 interior and foreign affairs ministers or their deputies are attending the two-day event, which started on Monday.

The world body said in a statement that the meeting aims to "produce a set of strategies and techniques to guide member states in their efforts” to address the issue of homegrown extremists traveling abroad to join terrorist groups such as the ISIL.

Between 25,000 and 31,000 such extremists have headed to war zones to join the ISIL, officials have warned. These include hundreds from European countries such as Britain, France, Germany, and Spain.

The ISIL terrorists have overrun huge swathes of territory in Iraq and Syria. They are engaged in crimes against humanity in the areas under their control. ISIL militants have terrorized and killed people of all communities, including Shias, Sunnis, Kurds, and Christians.

The event will also focus on the ways to prosecute and rehabilitate those who return.

Last year, the UN Security Council adopted a resolution, calling on member states to take measures to stem the flow, fearing that they may return to launch attacks in their home countries.