President Barack Obama and his allies sought to convince cautious lawmakers and the public of the need to strike Syria although officials conceded on Thursday they lacked conclusive evidence that President Bashar al-Assad ordered his forces to use chemical weapons against civilians.

Obama’s top national security officials were due to brief Congress on Syria later on Thursday and Britain said armed action would be legal, but any intervention looked set to be delayed until U.N. investigators report back after leaving Syria on Saturday.

Syrian opposition sources said Assad’s forces had removed several Scud missiles and dozens of launchers from a base north of Damascus, possibly to protect them from a Western attack, and Russia was reported to be moving ships into the region.

But expectations of imminent turmoil eased as the diplomatic process was seen playing out into next week, and the White House emphasized that any action would be “very discrete and limited,” and in no way comparable to the Iraq war.