Russia's Defense Ministry said on Thursday that two U.S. aircraft had bombed the Syrian city of Aleppo on Feb. 10, and that Russian planes had not been operating in the area.

A Pentagon spokesman had accused Russian and Syria regime forces on Wednesday of destroying Aleppo's two main hospitals with air strikes, though he did not specify when the strikes were alleged to have taken place.

The regime army has made rapid advances near Aleppo in recent weeks with the help of Russian air strikes.

But Defence Ministry spokesman Igor Konashenkov said in a statement that "only aviation of the anti-Daesh coalition flew over the city yesterday", referring to the U.S.-led alliance of countries fighting the Daesh terrorist group.

"At 1355 Moscow time, two U.S. Air Force A-10 attack aircraft entered Syrian airspace from Turkish territory. Reaching Aleppo by the most direct path, they made strikes against objects in the city."

He said the Russian targets on that day had been at least 20 km (12 miles) from the city.

When asked on Wednesday whether the U.S.-led coalition could do more to help rebels in Aleppo or improve access for humanitarian aid to the city, Pentagon spokesman Colonel Steve Warren said that the coalition's focus remained on fighting Daesh, which was "virtually non-existent in that part of Syria".

Capturing Aleppo, Syria's biggest city before the war but now divided between rebel- and regime-held sectors, would represent a major military victory for Syria's Bashar Assad and a symbolic prize for his ally, Russia, to help justify its bombing campaign in Syria.

Members of the United Nations Security Council pressed Russia on Wednesday to stop bombing Aleppo in support of the regime military offensive and allow humanitarian access ahead of a meeting of major powers in Germany on the conflict.

The Syrian army, supported by Russian air strikes, began a push to retake Aleppo and surrounding areas up to the Turkish border at the start of February.

Russia first began its air campaign in Syria on Sept. 30 of last year.

While Russia claims its campaign is aimed primarily at the Daesh militant group, it has repeatedly targeted civilian areas and the moderate anti-regime opposition groups that control them.

Syria has remained locked in a vicious civil war since early 2011, when the Assad regime cracked down on pro-democracy protests -- which had erupted as part of the "Arab Spring" uprisings -- with unexpected ferocity.