BEIRUT — Russian missiles pounded opposition targets in Syria on Tuesday, the start of a much-anticipated offensive, while activists reported the resumption of bombing in rebel-held neighborhoods of Aleppo for the first time in nearly a month, apparently by Syrian government warplanes.

The Russian blitz began hours after President Vladimir Putin and U.S. President-elect Donald Trump discussed Syria in a phone call and agreed on the need to combine efforts in the fight against what the Kremlin called their No. 1 enemy – “international terrorism and extremism.”

Russia said its offensive, using long-range missiles and its carrier-borne jets in combat for the first time on opposition areas in Syria, focused on rebel-held northern Idlib province and parts of the central province of Homs. It didn’t mention the besieged eastern neighborhoods of Aleppo.

The new offensive was a sharp snub to the Obama administration and its policy toward Syria, and augurs a major escalation in the coming days that would put tens of thousands of civilians in serious danger.

Months of negotiations between Moscow and the Obama administration have failed to cement a long-term cease-fire in Aleppo, which has become the focus of the war between President Bashar Assad and rebels fighting to topple him, some of whom receive U.S. aid. Al-Qaida’s Syrian affiliate is fighting alongside the rebels, but the Islamic State group has no presence in Aleppo.

In announcing the start of what he called “a major operation,” Russian Defense Minister Sergei Shoigu said it would target positions of the Islamic State group and al-Qaida’s Syrian affiliate in Idlib and Homs provinces.