The American School of Oriental Research's Cultural Heritage Initiative posted pictures from the satellite imagery and analytics company DigitalGlobe that show the construction on the edge of the ancient site that was damaged by the Islamic State group, which held Palmyra for 10 months.
Syrian troops backed by Russian airstrikes captured Palmyra in March and fighting continues miles away until this day.
Maamoun Abdulkarim, head of the Antiquities and Museums Department in Damascus, told The Associated Press that the Russians are building small barracks that includes offices and clinics.
Abdulkarim said his organization was not asked for permission but added that IS is close to the town and the presence of Russian and Syrian troops is important to ensure that the site remains in government hands.
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Since Russia began launching airstrikes in Syria in September 2015, Moscow has tipped the balance of power in favor of President Bashar Assad's forces. Earlier this year Russia said it was scaling back its presence in Syria.
Before IS captured the town in May 2015, the Syrian army was known to have minor military presence inside the site.
"During the time of war, sometimes archaeological authorities don't have a say but security decisions dictate the orders," AbdulKarim said. "Once the situation improves and peace is reached, then we will openly call for removing" the barracks.