Russia moves artillery in Syria near Aleppo, stoking concern: U.S.

Although Russia pulled out about half of its fixed-wing aircraft in mid-March, it broadly preserved its capabilities within Syria and remains a potent military force in support of Syrian President Bashar al-Assad, U.S. officials say.

Analysts said the Kremlin had changed rather than diluted its military power by increasingly relying on helicopters to support the Syrian army.

The U.S. official, who spoke on condition of anonymity, said the repositioning of artillery and some forces near Aleppo followed the Syrian government's recapture of the city of Palmyra from Islamic State.

The opposition accuses the government of violating the cessation of hostilities to capture Aleppo, Syria's most populous city before the war, which has been divided between government-controlled and rebel-held zones for years.

U.S. officials have noted a significant presence of the al Qaeda-linked al Nusra Front around Aleppo. Al Nusra is not included in the cease-fire agreement.

(Reporting by Phil Stewart)