(AFP) Jordanian King Abdullah II has vowed to hit back with "an iron fist", after a suicide bomber killed six Jordanian soldiers Tuesday near the Syrian border where thousands of refugees are stranded.
There was no immediate claim of responsibility but Jordan is part of the US-led coalition fighting the Islamic State (IS or ISIS) jihadist group in Syria and Iraq, and has been targeted by jihadists before.
The army said in a statement that the dawn bombing killed four border guards, one member of the security services and one member of the civil defense. Fourteen soldiers were also wounded.
It said that the suicide bomber set off from a makeshift Syrian refugee camp in no man's land near the Rukban border crossing in Jordan's remote northeast.
The driver entered Jordanian territory through an opening used for humanitarian aid deliveries and blew himself up as he reached a military post, it added.
Jordan hosts hundreds of thousands of Syrian refugees and thousands more have been stranded at the frontier since January.
King Abdullah condemned the attack and said that Jordanian armed forces would strike back.
"Jordan will respond with an iron fist against anyone who tries to tamper with its security and borders," the king said as he met with senior military and other officials.
"Such criminal acts will only increase our determination to confront terrorism and terror gangs that target army personnel who protect the security of the country and its borders," he said.
Tuesday's bombing comes two weeks after a gunman killed five Jordanian intelligence officers in a Palestinian refugee camp north of the capital.
A suspect was later arrested but details of the attack have been kept under a gag order while the investigation continues.
Jordan is a key member of the US-led coalition against ISIS and has carried out air strikes targeting the jihadists in Syria since 2014, as well as hosting coalition troops on its territory.
One of its pilots, Maaz al-Kassasbeh, was captured by the jihadists when his plane went down in Syria in December 2014 and he was later burned alive in a cage.
His murder prompted Jordan to extend its air strikes against ISIS to neighboring Iraq, where it is the only Arab coalition member participating in the bombing campaign.
In March, Jordanian authorities announced they had foiled an ISIS plot to carry out attacks in the kingdom in an operation that led to the deaths of seven jihadists.
The US embassy in Amman denounced Tuesday's bombing and pledged "unwavering support" for the armed forces of its key ally.
"We join the Jordanian people in their resilience and determination in the face of this cowardly terrorist act. The United States stands together with Jordan," it said.
Tens of thousands of Syrians fleeing their country have been stuck in makeshift camps in no man's land between the Syrian and Jordanian borders since January.
A flare-up in Syria's war sparked a new influx of refugees in the area last month, with nearly 5,500 arriving at Rukban within days in early May, bringing the total to more than 60,000.
Amman insists newcomers must be screened before entering the country to ensure they are genuine refugees and not jihadists from ISIS or Al-Qaeda trying to infiltrate the country.
The kingdom's position has drawn criticism from the office of the UN High Commissioner for Refugees (UNHCR).
UNHCR representative Andrew Harper said he was not aware of any Syrian asylum-seekers being hurt in Tuesday's attack.
Jordan says it hosts nearly 1.4 million Syrian refugees, of whom 630,000 are registered with the United Nations.
Their presence has placed a massive strain on Jordan's economy and resources, and raised security concerns in a country which has already experienced several jihadist attacks.
According to sources close to Islamists, almost 4,000 Jordanians have joined jihadist groups in Iraq and Syria, where an estimated 420 have been killed since 2011.