The agreement to establish cease-fires to allow aid delivery was the sole accomplishment of the last round of Syria peace talks, but the first mission in Homs was marred by violence.
What allowed Iran and world powers to reach an agreement was avoiding matters where interests diverge -- like Syria.
US Secretary of State Kerry and Russia's Foreign Minister Lavrov say they hope to convene an international conference on Syria later in May. The US has also stepped up humanitarian aid.
The bar is set high, but the US could begin providing body armor, night-vision goggles, rifles, and other basic arms to Syria's rebels.
Syrian Foreign Minister Walid al-Moallem said in Moscow that the Assad government wanted to engage in 'dialogue with anyone who's willing for it, even those who carry arms.'