AMMAN, Jordan — In a stretch of rocky desert between Jordan and Syria, around 12,000 refugees have become unwitting pawns in a high-stakes game of border politics.

According to satellite photos released by Human Rights Watch, thousands of Syrians fleeing war have bottlenecked in a demilitarized strip of land on the far east of the border between the two countries. Here, two man-made earthen berms run along the frontier, separated by a no man’s land several kilometers wide. Admissions into Jordan are few and far between — and a humanitarian crisis is building in the area, with diseases running rampant and several children having already lost their lives.

For months, humanitarians have cataloged swelling numbers of displaced people massed along the border. Most are clustered near the far eastern Ruqban crossing point, roughly 60 miles from the Iraqi border, while around 1,000 are near a crossing point called Hadalat just west of there. Syrians from eastern areas like Deir Ezzor usually arrive in Ruqban, while those in the west — fleeing violence in places like Homs and Hama — funnel down to Hadalat. Islamic State militants, Syrian government, coalition, and Russian airstrikes, hunger and exhaustion are just a few of the threats these people have faced on their southward odyssey.

Yet they keep coming. In late September, humanitarians counted 3,000 people at the berms. The figure had increased to 4,400 by Oct. 20, and on Nov. 4, a major NGO circulated an internal memo highlighting the plight of 5,070 people, most of them women and children, stranded in the area.

“The situation at the berm is quite alarming,” the memo reads. “Weather conditions are quite difficult these days, with rain and low temperature[s]. Very dire conditions, especially for 556 infants!”

Yet the Syrians continued to stream south, in far greater numbers than Jordan was allowing in. Aid officials say that from late November, the population at the berms leapt by more than 1,000 people each week. On Nov. 26, they say, Jordan ceased admitting even the small trickle of refugees it had allowed before, which was roughly 50 people per day. As aid organizations began to go public about the crisis, Jordan opened its doors for the first time in 10 days, admitting fewer than 50 people on Dec. 6, and around 100 on Dec. 7 — figures that are still smaller than the rate of arrivals to the no man’s land.

“Conditions are horrific,” said a senior aid official, who had been to the berms recently. “While it is easy to talk about numbers, it is only when you get up there in the dust and filth do you understand the desperation of the refugees.”

People are sleeping in makeshift shelters, under roofs of blankets stitched together with tarpaulins, the official said. Another aid worker who had been to the scene described “human waste everywhere.”

Illnesses have spread like wildfire. Scabies and dysentery have been documented by the NGOs that are granted access to the area, and in a statement on the crisis, officials from UNHCR noted that women have given birth at the berms, in squalid and unhygienic conditions. The assistance reaching the refugees is minimal: NGOs provide one meal a day, some nappies, and medication, which is delivered by the Jordanian armed forces that manage access to the area.

People have also died — a least 10 in the last several months. Some were older people dying of illnesses or heart defects, but at least a handful have been children.

Details of what’s actually going on in the no man’s land are hard to come by. Few diplomats and humanitarians are willing to criticize Jordan’s response on the record, for fear of damaging relations with their host government and losing access. Instead, they speak anonymously.

“The vast majority [are] women and children who are fleeing the bombing and the horror of ISIS with the expectation of finding safety in Jordan only to be held back,” said the senior aid official, who had been to the area recently.

Jordan denies the situation is as dire as aid agencies allege.

“The number of stranded refugees is exaggerated,” said government spokesman Mohammad al-Momani. “Our borders are open to refugees, and we announce arrivals on a daily basis.”

That openness is more a label than a reality: Jordan’s perimeter is tightly controlled by the military, and refugees’ access is closely managed. The country began implementing tight restrictions on entry last year and, since April, has actually seen more refugees leave the country than arrive.

Momani said that Jordan is hosting 1.4 million refugees from the Syrian conflict — the U.N. refugee agency says more than 600,000 have registered with it — and is working hard to alleviate the humanitarian crisis. But he also noted that Jordan “has its security and screening considerations for those who come in asking for refugee status.”

Jordan’s security argument — that the kingdom has to limit who comes in, for fear of upsetting its fragile domestic peace — has gained some traction in recent weeks. A string of unconnected incidents has raised fears that security in the country may be fraying: In late September, a police officer was shot and killed in an ambush in the central neighborhood of Jabal Amman. On Nov. 9, a Jordanian police captain opened fire at a U.S.-funded police training center, killing two Americans, a South African, and two Jordanians. While officials denied any extremist link, thousands of mourners chanted “Death to America” at his funeral. All the while, insiders and state media speak of foiled infiltration attempts by smugglers, drug dealers, or other individuals along the northern border with Syria.

“I think that there is a security issue; I am quite sure of this,” said a European diplomat. “A lot of attempts to carry out attacks have been thwarted at the border.”

The diplomat suggested that Jordan was trying to send a message by letting the refugees pile up on the Syrian border. “Keeping people on the berm is a way for Jordan to say that this is the responsibility of the international community, that it is causing economic and security problems.”

Another high-ranking European diplomat described the current situation as “a nightmare” for Jordan. “They don’t want to set a precedent and create a pull-factor so more refugees come,” the diplomat said. “They also just don’t want any more Syrians in Jordan.”

Jordan’s security agencies have struggled to maintain stability at home amid the increasing chaos in the region. But the question many observers are asking is why, given the country’s security and intelligence prowess, it isn’t willing to allow vetted people into the country when there is plenty of space at the U.N.-run and funded Azraq refugee camp, which currently hosts 28,000 people but can hold twice that number.

“It’s difficult to know how the security concern works, because we know that 80 percent of the refugees on the berm are women and children, sick, elderly, or wounded,” the senior diplomat said

As Russian and coalition airstrikes look set to increase and the war in Syria shows no signs of abating, the flow of people to Jordan is unlikely to slow anytime soon. Several aid agencies say their sources inside Syria warn of an even more dramatic increase in the number of people heading to the berms in the coming weeks.

As temperatures drop to around zero each night and the prospect of snow looms, the senior aid official fears worse days are yet to come.

“In a little while, the numbers on the berm are going to be bigger than Azraq.”