Between March and April at least 14 Tunisians self-detonated in Iraq alone, jihadis from Egypt, Libya, Morocco, Jordan, Britain, and Denmark also blew themselves up in Syria and Iraq.

(Reuters) – Shortly before Abdul Waheed Majeed, a 41-year-old British truck driver, blew himself up in an attack on a Syrian prison, he brushed aside a question in Arabic.

“I’m sorry, I can’t speak it,” he said in a video. “My tongue bro’… it’s got like a knot in it.”

That suicide-bomb attack on February 6 by the Pakistani-born Majeed, appeared to be part of a resurgence of such attacks that represented a disturbing shift in tactics among radical jihadists in the sectarian killing grounds of Syria and Iraq.

Many of them have been carried out by foreigners drawn to the conflicts from across the region and from Europe, U.S. and European security and intelligence officials say.

Will McCants, an expert at the Brookings Institution think tank in Washington, said given the rapid increase of foreign fighters in Syria “if the war drags on, the number of fighters will far eclipse those we saw in Afghanistan.”

The security officials estimated that several thousand foreign nationals are active in the two countries.

Most are with the Islamic State of Iraq and the Levant (ISIL), an ultra-conservative militant group reconstituted from an earlier incarnation of al Qaeda and is active in Syria and Iraq and with Jabhat al Nusrah, an al Qaeda affiliate which is one of the most powerful rebel forces in Syria.

In the last year the rate of suicide bomb attacks in Iraq has risen sharply, back to levels not seen since 2007, U.S. officials said.

The officials said they did not have precise data on the number of foreign fighters involved in the violence. But in March and April alone, at least 14 Tunisians fighting with ISIL blew themselves up at various locations in Iraq, according to postings on social media sites affiliated with ISIL, which U.S. and European authorities monitor.

That is about half of the total number of foreign suicide bombers identified with ISIL on social media who blew themselves up during the two-month period, said Laith Alkhouri, a senior analyst with Flashpoint Partners, a group which monitors militant social media postings.

Other suicide bombers in Iraq in March and April included fighters from al Qaeda in the Arabian Peninsula, one of the group’s most lethal wings based mostly in Yemen.

Alkhouri said many of them appeared to be Saudis, Libyans, Egyptians, Moroccans and Jordanians. A Danish citizen and a Tadjik were also reported by the group to have blown themselves up.