In stifling heat with minimal shelter and little access to food and water, some 70,000 refugees fleeing Syria's civil war have gathered at the Rukban border crossing in Jordan's remote northeast.
For months they have been dependent on food and water from international aid agencies but since last week's attack have been cut off.
Aid groups are alarmed but Jordanian authorities say the camp has become a hotbed of jihadist activity and security needs to come first.
"Since the attack... all humanitarian activities at the border were suspended until further notice," said Shaza Moghraby, a spokeswoman for the UN World Food Programme in Jordan.
She said there was deep concern for the refugees "who are enduring very harsh weather conditions, sweltering heat and frequent dust storms" and "have or are running out of food".
Rukban is a key crossing into Jordan for refugees fleeing Syria's five-year civil war, which has killed more than 280,000 people and forced millions from their homes.
There has been an influx of people to the area since fighting intensified late last year in central and eastern Syria but, after accepting waves of refugees earlier in the conflict, Jordan is now being more cautious about allowing them in.
Amman insists newcomers must be screened before entering the country to ensure they are genuine refugees and not jihadists from IS or Al-Qaeda.
- 'Security must take precedence' -
Jordan is a member of the US-led coalition battling IS in Syria and Iraq. It has carried out air strikes targeting the jihadists and hosts coalition troops on its territory.
Many of the refugees have set up camp inside a no man's land between the Syrian and Jordanian borders, from where they were able to receive assistance.
The Jordanian army said last Tuesday's attack saw the suicide bomber set off from the camp in no-man's land in an explosives-laden vehicle and blow it up at a military outpost, killing seven soldiers.
Jordan responded by declaring the remote desert regions "closed military zones", with no access to civilians including aid workers.
IS claimed responsiblity for the attack and authorities had no choice but to seal off the area, government spokesman Mohamed Momani said.
Signup to our newsletter and follow us on Facebook and Twitter!
"National security must take precedence over any other consideration," Momani told AFP.
"The zone where the refugees are gathered has become an enclave for Daesh on our borders," he said, using an Arabic name for the jihadist group.
The WFP, which previously had been providing food parcels including canned goods, bulgur wheat, rice, cooking oil, fruits and vegetables to the refugees, has since been unable to make any deliveries.
Perhaps more worrying, aid workers say, is the lack of water deliveries to the camp, where summer temperatures can often exceed 40 degrees Celsius (104 degrees Fahrenheit).
Since the attack, aid groups have only twice been able to deliver water to the camp -- which is dozens of kilometres (miles) from the nearest source in Syria.
The UN children's agency UNICEF was able to bring a water tanker to the area on Monday, Andrew Harper, the Jordan representative of the UN High Commissioner for Refugees, said on Twitter, but "food (is) still a massive concern."
- 'Lives at risk' -
Hala Shamlawi, a spokeswoman for the International Committee of the Red Cross (ICRC) in Jordan, said it was unclear how long the area would be sealed off.
"We are looking at other solutions," she said, adding that criminal gangs were taking advantage of the crisis to sell water and food at exorbitant prices.
"These difficult conditions could push those blocked to return to the interior of Syria," Shamlawi said.
Amnesty International last week warned Jordan that "a total closure of the border and denial of humanitarian aid to the area would inevitably lead to extreme hardship among those unable to find refuge and put their lives at risk."
Gerry Simpson, who handles refugee questions for Human Rights Watch, said Amman needed to be held responsible for the refugees' welfare.
"It is Jordan's choice to trap these people in the desert at its border... And any harm that comes to those people in that area as a result of dehydration, or lack of food and medical care, is fully Jordan's responsibility," he said.
Jordanian authorities have rejected criticism of the country's policies, pointing out that it already hosts nearly 1.4 million Syrian refugees, of whom 630,000 are registered with the United Nations.
Caring for refugees is "the responsiblity of the international community and not just of Jordan," government spokesman Momani said.
"The kingdom will cooperate as much as it can in the framework of these efforts," Momani said, adding that there were "other ways to bring aid to refugees without passing though the (Jordanian) borders."