The Pentagon is casting a skeptical eye toward Russian government claims that its airstrikes hit more than 1,000 Islamic State oil tankers in just a few days.

One U.S. defense official told Fox News it would be “nearly impossible” to destroy that many tankers with the kind of unguided bombs used by the Russians.  

The claims were first made Monday morning. Russian news outlet RT reported online that Russian strikes “torched” more than 1,000 tankers delivering crude oil to ISIS over a five-day period, citing a spokesman for the Russian Defense Ministry. The Russian Air Force, according to the report, also hit 472 targets in two days in Syria.

The claims come as the U.S. also says its coalition is hitting a large number of tanker trucks – albeit nowhere near as many strikes as Moscow says it conducted.

The U.S.-led coalition reported hitting 283 vehicles in eastern Syria on Nov. 21. Fox News has confirmed the vehicles were in fact oil tanker trucks.

Another defense official who spoke with Fox News said that the U.S. and Russia are not bombing the same targets.

“It’s hard to verify the effectiveness of Russia strikes without diverting assets,” the official added. 

But asked if the U.S. took the Russian claims at face value, the official said: “It’s Russia. They have proven to manipulate information in the past.”

As for the U.S.-backed coalition strikes, the attack by four A-10 attack planes and two AC-130 gunships was carried out Saturday at a site near Deir el-Zour and al-Hasakah but not reported until Monday. It followed a similar assault on Nov. 15 that destroyed 116 tanker trucks and is part of a broader air campaign, dubbed Operation Tidal Wave II, designed to cripple the militants' oil producing, refining and distribution system. The U.S. has said oil provides about half the group's total income.

Until the Nov. 15 strike, the U.S. had refrained from attacking oil trucks, fearing it could cause unintended civilian deaths.

The U.S. still is trying to avoid civilian deaths.

This time, U.S. aircraft dropped warning leaflets and made strafing runs in the area to persuade the civilian drivers of the tanker trucks to abandon their vehicles before the bombing began, military spokesman Col. Steve Warren said, adding that the U.S. believes no civilians were injured or killed.

ISIS controls nearly all of Syria's oil fields, concentrated in the east of the country, producing some 30,000 barrels a day, along with one field in Iraq. It smuggles the oil mainly to Turkey, selling at cut-rate prices and generating nearly $50 million a month.

Warren last week described Russia’s past airstrikes as “reckless” and not the kind of precision strikes used by the coalition. He said Russia was using “dumb” bombs to carry out the majority of its strikes against ISIS.

Fox News’ Lucas Tomlinson and The Associated Press contributed to this report.