Almost eight years into Syria's war, neighbouring Lebanon hosts around 1.5 million Syrians, many of whom live in the east of the tiny Mediterranean country.

On Wednesday, the army in the Arsal area detained "33 people with arrest warrants, 56 people without identity papers, and 300 others over expired documents", it said in a statement.

The military source said all were Syrians, and that those with no or out-of-date documents had been handed over to the security forces.

Those arrested had "committed an action against the law", they told AFP, without providing any further details.

Lebanon's army from time to time sweeps down on Syrian refugee camps, especially those in the east of the country.

Tens of thousands of Syrians live there, many from towns and villages on the other side of the Syrian-Lebanese border.

Arsal mayor Basel al-Hojeiri said that some of those who had been detained on Wednesday were then released overnight, complaining that the way in which the raids were carried out was "not right".

"They come to arrest a certain number of wanted people, and end up detaining 400," he said.

"They detain this huge number to then determine which ones are wanted among them, when it would be much better if they directly arrested those they wanted without bothering everybody else," Hojeiri said.

Last year, the army detained dozens of Syrians in mass raids on camps in Arsal, sparking a controversy after it announced four of them had died in custody.

Images circulated on social media showed dozens of bare-chested men lying down on the ground under the scorching sun with their hands tied.

Rights organisations demanded an investigation into the cause of their deaths.

Many Syrians live in tough conditions in Lebanon, and depend on international aid organisations for their survival.

Since the start of the year, around 8,000 Syrians have gone home from Lebanon, according to an AFP tally of official figures.

Lebanese security forces however claim tens of thousands have taken part in these returns, which are coordinated between Beirut and Damascus.

They waive late fines for those whose residency papers have expired if they agree to return to Syria.

The Syrian conflict has killed more than 360,000 people and forced millions from their homes since it started with the brutal repression of anti-government protests in 2011.