US Secretary of Defense James Mattis has apologised after Indonesia's army chief was denied entry into the US. Washington's ambassador to Indonesia has also issued an apology over the incident.

Indonesian army chief Gatot Nurmantyo was scheduled to travel to Washington on Saturday (21 October) to take part in a security conference on 23 and 24 October. When Gatot was attempting to board the US-bound Emirates flight, he was told by an airlines' representative that he has been barred from entering the US.

"A moment before departure, there was a communication from the airline that US Customs and Border Protection would not allow the TNI [Indonesian military] chief and his wife to enter US territory," a spokesperson for the military told reporters in Jakarta.

Gatot, accompanied by his wife, was invited by the Chairman of the US Joint Chiefs of Staff General Joseph Dunford to take part in the "Chiefs of Defense Conference on Country Violent Extremist Organizations."

President Joko Widodo, Foreign Minister Retno Marsudi and Chief Security Minister Wiranto have all been informed about the incident immediately after Gatot was stopped at the airport.

Following the embarrassing episode, Mattis offered an apology to Indonesian Defence Minister Ryamizard Ryacudu when they met in the Philippines on Monday, 23 October. "Minister Ryamizard accepted the apology that was conveyed during the short bilateral meeting," the Defence Ministry spokesperson Totok Sugiharto told the Jakarta Post.

The American diplomatic mission in Indonesia said it is prepared to facilitate Gatot's travel in the future and insisted the US remains committed to its strategic partnership with the country.