The number of Europeans joining Islamist fighters in Syria and Iraq has risen to more than 3,000, the EU's anti-terrorism chief has told the BBC.

Gilles de Kerchove also warned that Western air strikes would increase the risk of retaliatory attacks in Europe.

US-led forces have launched nearly 200 air strikes against Islamic State (IS) militants in Iraq since August and on Monday began targeting IS in Syria.

The UK parliament is due to vote on possible air strikes in Iraq on Friday.

IS has seized large parts of Iraq and Syria in recent months.

Mr de Kerchove said the number of 3,000 included all those who have been to the region, including those who have returned and those who have been killed there.

The CIA estimates that IS may have up to 31,000 fighters in Iraq and Syria - three times as many as previously feared.

Mr de Kerchove said that Islamic State's declaration of a caliphate in June may have played a role in drawing more support from Europe.

"If you believe in this, probably you want to be part of it as early as possible," he said.

He warned that air strikes by the US and its Western allies had increased the risk of a violent response from militant Islamists against European targets.

"I think we have to acknowledge that it will," he said.

"That was clear with the French because three days ago [IS] issued a statement saying there would be retaliation against the coalition. A French man was kidnapped in Algeria and he has been beheaded. So they did what they announced."

Source: BBC