The Wall Street Journal reports: Russia has been moving artillery units to areas of northern Syria where Assad government forces have been massing, raising U.S. concern that the two allies may be preparing for a return to full-scale fighting after a nearly two-month cease-fire with the main opposition, U.S. officials say.

The recent Russian redeployments within Syria have been accompanied by the return of some Iranian army forces to government-controlled areas close to the front lines, according to officials briefed on the intelligence. Russia, Iran and the Lebanese movement Hezbollah have been President Bashar al-Assad’s main supporters in the conflict.

U.S. concerns about the Russian buildup in northern Syria, and the negative impact it could have on the cease-fire and political negotiations in Geneva, prompted President Barack Obama’s call to Russian President Vladimir Putin on Monday, officials said.

Josh Earnest, the White House press secretary, used unusually harsh language in describing the exchange between the two leaders, calling it an “intense conversation.”

Russian officials have voiced support for the partial cease-fire and the United Nations-mediated negotiations in Geneva, both in public and in private settings, according to U.S. officials.

But both are on the verge of complete collapse. Citing widening attacks by government forces, representatives of the main opposition broke off the latest round of indirect talks on Monday. Government forces have stepped up attacks in some areas in northern and central Syria in recent days, and one opposition negotiator on Tuesday described the truce as over. [Continue reading…]