A Jordanian officer shot dead two US government security contractors, a South African trainer and a Jordanian translator at a US-funded police training facility near Amman yesterday before being killed in a shootout, authorities said yesterday.

US President Barack Obama said he was treating the attack at the King Abdullah Training Centre – in which four Jordanians and one Lebanese citizen were wounded – very seriously and a full investigation was under way.

The gunman was a police captain, a senior Jordanian official said. There was no immediate word on the attacker’s background or motive. But Jordan is a staunch US ally in the Washington-led campaign against Islamic State militants who hold large areas of neighbouring Syria and Iraq, a position Jordanian officials say leaves the kingdom vulnerable to jihadist attacks.

The US Embassy in Amman said two American civilian security contractors and a South African contractor were shot to death, and the slain Jordanian was a translator according to the Jordanian government.

Jordanian government spokes-man Mohammad Momani denied an assertion by three US government sources later yesterday that eight people were killed in the incident, reiterating that five had died including the gunman. One of the wounded was in critical condition, he said. A US official said the two Americans were working for the US.State Department’s International Narcotics and Law Enforcement Affairs Bureau training Palestinian security forces.

Mr Obama told reporters at the White House: “The fact that someone dressed in military uniform carried out an attack at a training facility in Jordan..., we take this very seriously, and we’ll be working closely with the Jordanians to determine exactly what happened.”

Security sources said several earlier militant plots to attack the King Abdullah training centre had been foiled. Mr Momani, the government spokesman, said the attacker was shot dead by Jordanian security forces inside the training centre. He did not commit suicide as security sources had earlier reported.

The training facility was set up on the outskirts of the capital Amman after the 2003 US invasion of Iraq to help rebuild the shattered country’s security forces and to train Palestinian Authority police officers.

Jordan hosts several hundred US contractors who are part of a military programme to bolster its defences, including the stationing of F16 fighter jets that use Jordanian airfields to hit Islamic State positions in neighbouring Syria.

But Jordan’s role in the war against Islamic State has raised disquiet among some Jordanians about instability at their borders. They fear that Amman’s enhanced role in the campaign might provoke Islamist bloodshed in their country.

Jordanian authorities have since tightened security around sensitive government districts, increased surveillance of radical Islamists and jailed dozens on suspicion of plotting attacks on Israelis, Americans and other Westerners.

King Abdullah believes fervently that ultra hardline jihadists pose an existential threat to the kingdom.