Jordan declared the desert border regions with Syria and Iraq "military zones" barred to civilians after a suicide bomber killed six Jordanian soldiers near the Syrian frontier on Tuesday.
King Abdullah II vowed to hit back with an "iron fist" after meeting top civilian and military officials to discuss the attack in an area where thousands of Syrian refugees are stranded.
There was no immediate claim of responsibility but Jordan is part of the US-led coalition fighting the Islamic State group in Syria and Iraq, and has been targeted by IS jihadists before.
The army said the dawn bombing killed four border guards, one member of the security services and one member of the civil defence. Fourteen soldiers were also wounded.
Jordanian soldiers carry the coffin of their comrade Belal Al-Zuhbi during his funeral in Nahleh village, near Jerash north of Amman, on June 21, 2016, after he was killed alongside five comrades in a suicide bomb attack on the border with Syria (photo by: Stringer/AFP)
It said 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 north.
The driver entered Jordanian territory through an opening used for humanitarian aid deliveries and blew himself up as he reached a military post.
King Abdullah condemned the attack and said Jordan's armed forces would strike back.
"Jordan will respond with an iron fist against anyone who tries to tamper with its security and borders," he said.
"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." 2
The Jordanian army said in a statement 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 before entering Jordanian territory (photo by: Stringer/AFP)
Soon after, the army issued a statement declaring Jordan's desert regions that stretch northeast to Syria and east to Iraq "closed military zones".
"We will deal firmly with any vehicle of individual that moves in the area without (prior authorisation) because they will be considered enemy targets," it warned.
The army did not explicitly say if the border with Syria would be closed.
But government spokesman Mohamed Momani told AFP the measure would not affect "humanitarian cases" -- a reference to refugees fleeing Syria's five-year war.
Jordan hosts hundreds of thousands of Syrian refugees and thousands more have been stranded at the frontier since January.
A map of Jordan locating a suicide bomb attack in Rukban (photo by: Laurence Saubadu, Vincent Lefai/AFP)
Tuesday's bombing comes two weeks after a gunman, who was later arrested, killed five Jordanian intelligence officers in a Palestinian refugee camp north of the capital.
Details of that attack have been kept under a gag order while the investigation continues.
Jordan is a member of the US-led coalition against IS. It has carried out air strikes targeting the jihadists and hosts coalition troops on its territory.
Maaz al-Kassasbeh, a Jordanian fighter pilot, was captured by the jihadists when his plane went down in Syria in December 2014 and he was later burned alive in a cage.
In March, Jordan announced it had foiled an IS plot to carry out attacks in the kingdom in an operation that led to the deaths of seven jihadists. 4
A Jordanian soldier carries a young Syrian refugee at Rukban camp (photo by: Khalil Mazraawi/AFP/File)
The US embassy in Amman denounced Tuesday's bombing and pledged "unwavering support" for the armed forces of its key ally.
"We join the Jordani an people in their resilience and determination in the face of this cowardly terrorist act. The United States stands together with Jordan," it said.
A flare-up in Syria's war last month sparked a new influx of refugees in the no man's land. Nearly 5,500 arrived at Rukban within days in early May, bringing the total since January 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 IS 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.
On Tuesday the Jordanian government spokesman said his country does not expect to build more refugee camps on its soil or extend those already there.
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.