Lebanese authorities have located human remains believed to belong to soldiers kidnapped by ISIL in 2014, according to a top security official.

The announcement on Sunday came hours after the Lebanese army declared a ceasefire deal with the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) armed group along the border with Syria in exchange for information on the missing soldiers.

The head of the General Security agency, Major General Abbas Ibrahim, said ISIL fighters who had surrendered led his agency and the Lebanese army to the remains.

"We have removed the remains of six bodies. We are expecting the number to go up to eight," he told reporters gathered in Lebanon's capital, Beirut.

"We believe that these remains belong to the soldiers."

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The troops were among 30 soldiers and police kidnapped by ISIL and al-Qaeda's former Syrian affiliate when they overran the Lebanese border town of Arsal in August 2014.

Four were killed by their captors and a fifth died of his wounds while 16 were released in a prisoner swap in December 2015.

The army has said the missing troops were its "top concern" in its offensive against an estimated 600 ISIL fighters in the hilly border region.

The missing troops were numbered at nine, but Ibrahim on Sunday only referred to the bodies of eight people and did not give details on a ninth.

He said the remains would be subject to DNA testing to ensure their identities but that he was "almost certain that the case is closed".

The top official spoke in downtown Beirut after informing the soldiers' families of the developments.

Relatives of the hostages had gathered for hours in the blistering heat to await news of their loved ones, sitting in tents they erected three years ago during protests to pressure the government to find the soldiers.

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Al Jazeera's Mohammed Jamjoom, reporting from Beirut, said the gathered family members were all "very sombre and downbeat".

"Certainly the mood was very grim," he said.

"These are family members that have been desperate to find for years now for the fate of their loved ones," Jamjoom added.

"That have worried for so long that their loved ones may be dead, but have also tried to hold out hope that by some miracle, perhaps, they would be found alive and returned to them safely."