Donald Trump. Scott Olson/Getty Images

President Donald Trump asserted that Mexico was ranked the "second deadliest country in the world" on Thursday evening and cited "drug trade" as the cause.

When homicide numbers are compared on a per-capita basis, Mexico's number of homicides per 100,000 people puts it on somewhat different ground, pushing it to the middle of the pack in Latin America.

The Mexican government was previously critical of the report, saying "Violence related to organized crime is a regional phenomenon" that goes beyond Mexico's borders.

President Donald Trump on Thursday evening tweeted that "Mexico was just ranked the second deadliest country in the world, after only Syria. Drug trade is largely the cause. We will BUILD THE WALL!"

Trump was likely referring to a recent study by the London-based International Institute for Strategic Studies that named Mexico the second-deadliest conflict zone in the world, behind Syria and ahead of Iraq.

The president retweeted a link to a CNN story about the report when it came out in early May.

However, that study was highly disputed, and a number of factors undercut the assertion. (It should also be noted that a wall would not stop much of the drug flow into the US, and that drug-related violence in Mexico has largely not spilled over into the US.)

According to the IISS report, Mexico's nearly 23,000 intentional homicide victims in 2016 fell short of the 50,000 seen in Syria and exceeded the 17,000 recorded in Iraq and the 16,000 registered in Afghanistan. The next country in the ranking — Yemen — was below 10,000 victims, and the following two, Somalia and Sudan, were both below 5,000.

As Trump said, organized crime related to the drug trade is behind much of Mexico's violence, and the IISS ranking put Mexico on its list because, in its estimation, criminal violence in the country had reached "a level akin to armed conflict."

A police officer stands outside the Blue Parrot nightclub after a gunman opened fire outside the venue, killing several people and injuring others, in Playa del Carmen, Mexico, January 16, 2017. REUTERS/Victor Ruiz Garcia

While Mexico did indeed have 23,000 intentional homicide victims in 2016 (and looks set to exceed that this year), not all of those deaths were related to organized-crime-related violence. According to research by the Justice in Mexico project, only about one-third to half of those deaths appear to be related to organized crime.

The IISS told Business Insider that it did not assess a more precise tally of organized-crime-related deaths because the Mexican government does not release it. (Indeed, it has been several years since such a figure was made public.) "If they released this number monthly, or at least annually, we would be happy to use it," the think tank said.

Moreover, the comparison made by the IISS is based on absolute numbers. By that measure, other countries in Latin America — one of the most violent regions of the world — are close to or surpass Mexico.

The basis of the measure on absolute numbers was also disputed by a number of observers, as homicide comparisons are more often made based on per-capita numbers — typically the number per 100,000 people.

A forensic team works at the crime scene where a body was found wrapped in a blanket in Ciudad Juarez, Mexico, September 11, 2016. REUTERS/Jose Luiz Gonzalez

Measuring homicides by absolute numbers puts Mexico close to or behind other countries in Latin America.

In Venezuela, one nongovernment organization counted more than 28,000 violent deaths in 2016, more than 18,000 of which the government there classified as homicides. In Brazil, the last several years have seen total homicide counts close to 60,000. Colombia recorded about 12,000 homicides in 2016, its lowest tally in 32 years.

By comparison, the US had 15,700 homicides in 2016, according to the FBI.

When homicide numbers are compared on a per-capita basis, Mexico's homicide rate puts it on somewhat different ground.

Homicide rates in Latin America through 2012-2014. UNODC/Justice in Mexico project

It falls to the middle of the pack just in Latin America. Comparatively, Mexico's 2014 homicide numbers put it behind all the countries of the Northern Triangle — Honduras, El Salvador, and Guatemala — as well as Brazil, Colombia, Venezuela, and small countries like the Dominican Republic and Jamaica. Mexico's official per capita homicide rate in 2016 was 17 per 100,00.

The IISS also told Business Insider in a statement that inclusion on the list was based on three criteria:

"1-Sustained wide-ranging threat to state authority through years (not just spikes) from well-armed groups. 2-Groups control territorial spaces in several cities or rural areas 3- armed forces deployed frequently or permanently."

By those standards, other countries in the region likely deserve inclusion but didn't make the list. In Brazil, large armed gangs fight each other and have retaliated against police operations with public violence, and in Venezuela, organized armed groups challenge the state's control in some areas.

A Brazilian army soldier patrols the Mare slums complex in Rio de Janeiro, April 5, 2014. Ricardo Moraes/Reuters

Those two countries and the countries of the Northern Triangle — which also deals with powerful criminal groups like MS-13 and Barrio 18 — have all, like Mexico, deployed their militaries and militarized police forces to combat violence.

"They cite countries like Brazil, which have higher homicide rates per 100k inhabitants. The rate is a different measure, which is usually released much later in the year and is not doable for the ACD/ACS (since many conflict countries are measured in absolute number of fatalities, not rate per 100k)," the IISS told Business Insider in a statement when asked about these criticisms.

"Plus, we don’t follow Brazil, Venezuela and others because they don’t quite fit the criteria above," the statement said. "There, criminal violence is much more fragmented and involves a great deal of micro-criminality, rather than heavy-calibre clashes for territories that we see in Mexico."

The Mexican government was critical of the report when it was first issued in May.

"Violence related to organized crime is a regional phenomenon" that goes beyond Mexico's borders, it said in a statement. "The fight against transnational organized crime should be analyzed in a comprehensive manner."

Members of the military police carry out a routine foot patrol at El Pedregal neighborhood Tegucigalpa, Honduras, May 3, 2017. Thomson Reuters

Other experts who study crime and violence criticized the comparison.

"Equating these [countries] with Syria is analytically lazy and lends itself to the wrong policies," Tom Long, a professor at the UK's University of Reading, said on Twitter. "They aren't mainly political conflicts."

"Yes there's tragedy in Mexico, but not accurate to suggest it's like Syrian war," Brian J. Phillips, a professor at the CIDE in Mexico City, said on Twitter, "and per capita other countries have much more violence."

While the report itself was enough to elicit frustration in Mexico, Trump's retweet of a Drudge Report tweet linking to a CNN story about the report added to the ire.

"I hope these morons are happy," Mexican security analyst Alejandro Hope tweeted. "Their idiotic report was already retweeted by @realDonaldTrump."