The number of migrants who died near the US-Mexico border rose in 2017 even as the number of attempted border crossings fell dramatically, according to the United Nations’ migration agency.

Last year, 412 migrant deaths were recorded on either side of the border, up from 398 a year earlier, the International Organization for Migration said, adding that 16 migrant deaths had already been recorded in the area so far in 2018.

“The increase in deaths is especially concerning, as the available data indicate that far fewer migrants entered the US via its border with Mexico in the last year,” Frank Laczko, head of IOM’s Global Migration Data Analysis Centre, said in a statement.

Last year, the US border patrol reported apprehending 341,084 migrants along the south-western border – a 44% drop from the 611,689 migrants apprehended in 2016.

Fewer migrants thus appear to be making the perilous overland journey to America from Central American and Mexico, in what has widely been attributed to harsh, anti-immigrant rhetoric from US President Donald Trump since he came to power in early 2017.

Migrants from Central America and Mexico willing to make the dangerous trip risk being victimised by thieves, criminal gangs and traffickers who sometimes take their money and abandon them in desperate conditions on either side of the US border.

Violence does not appear to be a main cause of migrant deaths near the border.

According to IOM statistics, only five of the deaths recorded last year were confirmed to be due to violence, such as blunt force trauma and gunshot wounds.

However, “there are a lot of bodies recovered which are skeletal or otherwise heavily decomposed on the border, so for many of the deaths we record we do not know the cause of death,” Julie Black, who coordinates IOM’s Missing Migrant Project, told AFP by email.

Gender can also be difficult to determine: while only 20 of last year’s victims were determined to be women, gender could not be determined in more than 100 cases, Black said.

Seven of the migrants who died last year were children, the IOM numbers show.

One major cause of death among migrants along the border in 2017 was the heavy rainfall early in the year that swelled the Rio Grande, making it more treacherous to cross.

In all, 91 of the migrants who died near the border last year drowned, up from 67 in 2016, the IOM statistics show.

Another 46 died from exposure and dehydration during warm months, when temperatures often top 40C (104F), while 18 died from hypothermia.