By Suleiman Al-Khalidi, Maya Gebeily

BEIRUT (Reuters) -As Wagner mercenaries advanced on Moscow in an attempted mutiny in late June, authorities in Syria and Russian military commanders there took a series of swift measures against local Wagner operatives to prevent the uprising spreading, according to six sources familiar with the matter.

The previously unreported crackdown included blocking phone lines, summoning around a dozen Wagner commanders to a Russian military base, and ordering mercenary fighters to sign new contracts with the Russian defence ministry or promptly leave Syria, according to the sources, who include Syrian security officials, sources based near deployed Russian forces, and regional officials.

The sources declined to be named in order to discuss sensitive military information. Syria's government, Russia's defence ministry and Wagner in Russia did not respond to requests for comment.

The measures showed how Syrian authorities moved quickly to bring the mercenary force to heel, worried that their key military partner Russia was distracted by events back home, according to two Syrian sources informed of the deployments.

"Wagner's role in Syria - as it was playing it before - is over," said Nawar Shaban, researcher at Omran Center for Strategic Studies, an Istanbul-based independent research group focused on Syria. "Given the events, their relationship with the Syrian defence ministry is now over."

Damascus has not publicly commented on the June 23-24 Wagner mutiny in which mercenary boss Yevgeny Prigozhin ordered his men fighting for Russia in Ukraine to march on Moscow before a deal brokered by Belarus saw them turn back and many exiled.

However, senior Syrian military and intelligence officials privately voiced concern as they watched events unfolding that the mutiny could disrupt the Russian military presence they had relied on for so long, according to a senior Syrian Republican Guard officer and a Syrian source briefed on developments.

The mercenary group's presence in Syria is relatively small at between 250 and 450 personnel, or roughly a tenth of the estimated Russian military strength, the two Syrian sources said. There are no official figures on staffing, which vary over time.

Russia deployed its military forces and, crucially, its airpower to Syria in 2015, helping President Bashar al-Assad beat back rebels intent on toppling him.

Wagner has since been involved in combat missions and security for oil installations in Syria, with the first suspected Wagner deaths there reported as early as 2015.

For years, Moscow denied any connection with Wagner, but the group has played a very public role in Russia's war in Ukraine. President Vladimir Putin said after the mutiny that his government funds the group.

After Prigozhin announced his uprising, a group of Russian military officers were quickly dispatched to Syria to help take charge of Wagner forces there, according to a regional military source close to Damascus and two Syrian sources with knowledge of the events, who did not provide further details.

Syria's military intelligence cut landlines and internet links overnight on Friday June 23 from areas where Russian Wagner forces were deployed to prevent them from communicating among themselves, with Wagner in Russia, and even with relatives back home, the three sources said.

By the morning of Saturday June 24, Syrian military intelligence and Russian defence officials were coordinating closely to isolate and control Wagner operatives, according to the senior Republican Guard officer, a Syrian security source and two Syrian sources briefed on the developments.

Around a dozen Wagner officers deployed in Syria's central province of Homs and other areas were summoned to Russia's operational base at Hmeimim in western Latakia province, according to the Republican Guard officer and one of the Syrian sources briefed on the developments. The officer said this occurred "in the early hours of the mutiny."

Reuters could not determine what happened to them. The Russian Reconciliation Center for Syria, headquartered in the Hmeimim base, refers all media enquiries to the defence ministry, which did not respond to requests for comment.

NEW CONTRACTS OR FLIGHTS OUT

By June 24, Wagner fighters in Syria were asked to sign new contracts by which they report directly to Russia's defence ministry, a source with knowledge of Wagner's deployments and two other sources with knowledge of the events said.

Their pay was also cut, those three sources said.

Those who refused the terms were flown out on Russian Ilyushin planes in the following days, two of those sources said. One said they numbered "in the dozens," surprising Syrian officials who expected more would refuse and head into exile.

Between June 25 and 27, flight-tracking data from Flightradar24 shows at least three trips by a Russian Ilyushin plane between Latakia, Syria and Bamako, the capital of the West African nation of Mali, where Wagner also has operations. Reuters could not establish whether Wagner personnel were on board the flights.

Mali authorities did not respond to a request for comment on the flights and whether any Wagner fighters had been redeployed from Syria to Mali.

Wagner had already pulled many experienced Russian fighters out of Syria last year to fight in Ukraine following Russia's full-scale invasion, according to Syrian analysts and a retired Syrian military officer familiar with Wagner activities.

Wagner fighters secured Syrian oilfields and Western officials say Wagner is linked to Evro Polis, a company that profits from those assets. The EU imposed sanctions on the firm in 2021.

Reuters was unable to determine the fate of those commercial interests in the wake of the Russian defence ministry's moves against Wagner in Syria and Russia. Evro Polis did not immediately respond to emails sent to a contact address on its website.

Hmeimim base has served as a logistics hub to transit Wagner fighters on to Libya and elswhere in Africa, according to a Syrian security source and a Western diplomat based in the region. "We are watching how those Wagner operations will in turn be disrupted," the diplomat said.

Unlike its other operations in Africa, where Wagner's presence is larger and not subservient to the Russian military, its role in Syria's war went little noticed at first, as Russian air power turned the tide of the conflict.

Details of its presence emerged gradually, notably in 2018 when hundreds of Wagner fighters were killed in a confrontation with U.S. forces near the Syrian city of Deir al-Zor, sources told Reuters at the time.

In the wake of the Wagner uprising, Syria's leadership quickly restated publicly the importance of its military alliance with Russia.

Syrian first lady Asmaa al-Assad was in Russia days later to attend her son's graduation from Moscow State University and was asked by a reporter whether she had been afraid to visit given recent events.

"Our Russian friends did not hesitate when they stood with us in our war. So we did not hesitate, and we won't hesitate, to stand with them in their war," she said.

(Additional reporting by Laila Bassam and Tom Perry in Beirut and Ed McAllister in and Joanna Plucinska in London; Editing by Mike Collett-White and Daniel Flynn)