There is more evidence that Russian forces are not pulling out of Syria, but instead, more troops are arriving there, a new video from Russian television Saturday apparently shows.
The video shows a convoy of Russian troops headed to Palmyra to begin mine clearance operations after ISIS was routed from there last week.
Col. Steve Warren, a U.S.-led coalition spokesman in Iraq, could not confirm that Russian "sappers" or engineers had arrived in Syria when asked at a Pentagon press conference Friday.
Russian jets and helicopter gunships helped Syrian forces push ISIS from Palmyra, once a popular tourist destination filled with ancient Roman-era artifacts, earlier this week.
A U.S. defense official tells Fox News that Syrian forces suffered "heavy losses" against ISIS, but would not offer any specifics.
In a statement from Russia's defense ministry posted on its website, the new Russian forces will conduct "humanitarian mine clearance" in Palmyra.
Russian President Vladimir Putin said in March that his main forces would begin withdrawing from Syria. Pentagon officials now say otherwise.
Critics point to a similar pledge from President Putin when Russian agreed to a ceasefire and to withdraw troops and equipment out of eastern Ukraine in 2014. The outgoing U.S. commander of NATO forces in Europe recently said Russian troops and equipment remain.
Despite sending less than half of its jet fighters back to Russia, there are now more Russian attack helicopters in Syria than at any time since the air campaign to shore up Syrian President Bashar al-Assad began in late September.
The Pentagon has not seen Russian aircraft fly from Syria to Russia since March 19, one official tells Fox News.
More than 20 fixed-wing fighter-bomber aircraft remain in Syria in addition to more than a dozen attack helicopters, including the newest gunship in Russia's arsenal, the Mi-28N "Havoc."
U.S. officials believe the deployment of Russian military forces to Syria is not short term.
"The Russians installed underground fuel tanks in their air base in Latakia. This was not a temporary move, but a permanent one," a defense official told Fox News.
The Russian Navy has occupied a Syrian port in Tartus since the early 1970s.
In Fall 2015, the Russians sent T-90 battle tanks, rocket-propelled artillery systems, and in December, the advanced S-400 air defense system to protect their new air base north of Tartus on the Mediterranean coast in Latakia. U.S. officials say all of these weapons remain as well.
After defeating ISIS in Palmyra, it is unclear if the Russian-backed Syrian forces will continue to the Islamic State's de-facto capital of Raqqa, only a three-hour drive from Palmyra, or head east to oil-rich Deir ez-Zor, the site of an Assad regime air base.
Warren did not expect an assault on ISIS headquarters in the near future.
"Nobody's going to get to Raqqa anytime soon, frankly, neither the Russians nor the SDF [Syrian Democratic Forces]," said Warren.
The U.S. military supports the Syrian Democratic Forces, which are made up of largely Kurdish fighters, but also Arab groups as well.
Russia has been accused of killing hundreds of civilians and destroying hospitals inside Syria. U.S. officials say Russia has conducted a majority of its airstrikes using unguided or dumb bombs, far less precise than the satellite-guided weapons used by the U.S. military.
-- Lucas Tomlinson is the Pentagon and State Department producer for Fox News Channel.