The number of suicide bombings around the world surged 94 percent last year amid the rise of the Islamic State in Syria and Iraq and the U.S. withdrawal from Afghanistan, the Tel Aviv-based Institute for National Security Studies says in a report to be published Sunday.

The INSS expects the trend to continue in 2015 due to the instability in several countries and the increasing number of religious and ethnic conflicts, as well as the growing strength of groups like the Islamic State and Al-Qaida.

Some 3,400 people were killed in such attacks last year, compared with 2,200 in 2013, a 37.5 percent increase. There were 592 bombings, compared with 305 in 2013, says the INSS, a research institute and think tank affiliated with Tel Aviv University.

The figures are estimates because of the heavy fighting in some regions where suicide bombings occur. Such attacks have become an especially common method for Salafi Sunni jihadist groups.

“Suicide bombings are not just an effective tactic for them in terms of their goal of causing death and destruction and establishing fear, but are also a commercial symbol and proof of the willingness of their activists to sacrifice themselves in the way of God,” the INSS says.

As in recent years, these organizations were responsible for most suicide bombings around the world in 2014. The claim that most suicide bombings are carried out against foreign occupiers has been proved false once again, the INSS says.

Only 3 percent of all suicide bombings were carried out against foreign armies, while most were conducted against government, military and local security-force targets, or based on religious or ethnic rivalries, the think tank says.

The study’s authors are Yoram Schweitzer, the head of the INSS’ program on terrorism and low-intensity conflict; research associate Einav Yogev; and Ariel Levin.

They use reporting from more than one source before labeling an incident a suicide bombing. They particularly have reservations about reporting from Syria, where media reports often lack details on the location and number of casualties.

Reports from Syria are often based on reports from the organizations behind the attacks, which often exaggerate. The authors say they have included “only attacks whose details could be verified.”

There was a significant rise in the number of suicide bombings in the Middle East last year: 370 attacks with some 2,750 dead, compared with 163 and 1,950 killed in 2013. This was especially notable in Iraq (271 attacks, up from 98), Yemen (29 attacks, up from 10), Lebanon (13 attacks, up from three) and Libya (11 attacks, up from one).

The number of suicide bombings in Syria remained at 41, though, again, the authors were cautious about that data. Four such attacks were carried out in Egypt compared with six the previous year. The non-Arab Muslim world — Afghanistan in particular as well as Africa — saw a rise in suicide bombings.

Fifteen suicide bombings in 2014 were carried out by women, compared with five in 2013.

There were three main causes behind the jump in suicide bombings last year: the continued upheaval in the Middle East that is rocking governments and strengthening non-state actors, the meteoric rise of the Islamic State, and the U.S. withdrawal from Afghanistan.

Much of the increase in the Middle East can be attributed to the rise of the Islamic State, also known as ISIS or ISIL, in Iraq and Syria. The declaration of the Islamic State and the establishment of the so-called caliphate in mid-2014 led to a major escalation in suicide attacks in which 382 bombers took part last year.

Many of the suicide bombers in Iraq were foreigners who volunteered for ISIS. The organization rarely took responsibility for bombings, but the authors say ISIS was responsible for the great majority of such attacks in Iraq.

Some 71 percent of suicide bombings in Iraq targeted the country’s security forces — whether roadblocks, bases, police stations or soldiers. Some 17 percent were aimed at civilians. This was the highest number of suicide bombings in Iraq since 2008; the attacks there made up 45 percent of all such attacks worldwide last year.

No deadly suicide bombings occurred in Israel or the Palestinian territories last year. Reports of Hamas using suicide attacks during the Gaza war were never confirmed.

Israel must prepare for the possibility that terror groups in neighboring countries will turn some of their efforts against it. Developments could encourage Israel’s enemies such as Hamas and Islamic Jihad to join such efforts this year.

The operations of Boko Haram stood out in Africa last year. The organization declared an Islamic emirate in Nigeria and was also responsible for kidnapping hundreds, including over 200 school girls who were forced to convert to Islam. Most are still being held hostage.

The suicide attacks conducted by Boko Haram — 32 killing some 500 people — made up half the number of such attacks the organization has carried out since it started using the tactic in 2011.