Despite fears rising globally about lone-wolf terrorist attacks inspired by extremists, more sophisticated foreign terrorist plots like those employing multiple forms of violence and direct involvement by terrorist organizations remain the deadliest threat, a new Homeland Security intelligence assessment concludes.

The assessment obtained by CNN analyzed 99 terror attacks linked to foreign terrorist organizations from 2014 to 2018, including events in North America, Australia and Europe. Only 24 of the incidents were in the US, but the assessment noted that similarities among Western countries still made the analysis useful.

According to the unclassified report by the Department of Homeland Security Office of Intelligence and Analysis, recent extremist efforts to promote lone-wolf attacks employing tactics like stabbings and vehicle ramming still aren't as effective -- measured by deadliness -- as more sophisticated attacks.

"We assess that, despite recent violent extremist messaging highlighting the use of edged weapons or vehicle ramming to conduct attacks, the successful employment of more sophisticated tactics and procedures — such as those involving multiple tactics, (terrorist organization)-directed and trained operatives, or improvised explosive devices (IEDs) — remains the most likely significant factor influencing an attack's effectiveness as measured by the number of deaths."

Speaking on the anniversary of the September 11, 2001, terrorist attacks on Tuesday, FBI Director Christopher Wray told CBS "This Morning" that there were 120 terrorism-related arrests in the US last year. He added that the threat today includes "all the kind of major terrorist organizations that you would think of" as well as domestic violent extremists that are already in the US and have been radicalized online.

According to the report, factors that increase the deadliness of an attack include planning attacks to exploit specific vulnerabilities in targets, including focusing on soft targets and planning attacks when areas are the most crowded.

One of the biggest single factors was whether the attack was directed by a foreign terrorist organization or inspired by it. According to the analysis, directed attacks in the study resulted in an average of almost 10 times as many fatalities.

The report notes exceptions, however, notably including the 2016 Pulse nightclub shooting in Orlando that killed 49 people.

The most fatal form of attack was firearms used on crowds, followed by vehicles rammed into crowds.

The report concludes that continuing to share threat and suspicious activity information among different levels of government and the private sector remains important.

The report also recommends dispersing security within crowds and trying to reduce the number of people crowded at security checkpoints at large events. It also suggests that first responders practice and plan how to respond to an attack, crediting such a plan with saving potentially hundreds of lives in the 2015 Paris attacks.

Asked for comment, a DHS official told CNN in a statement, "We routinely work with federal partners as well as state and local law enforcement, through the National Network of Fusion Centers, to assess all threats and analyze trends to allow our partners to mitigate against and respond to any threats to the Homeland."