The Arab League suspended Syria's membership at the end of 2011 following months of brutal repression of anti-regime demonstrations and an opposition movement supported by Gulf monarchies.
But Arab League chief Ahmed Aboul Gheit, speaking at the same press conference, ruled out an early return of Syria to the Cairo-based organisation.
Any decision was up to the League's 21 other members, he said, adding that the issue was not on the current agenda and would only be raised when "a political settlement" was in sight for Syria's almost six-year-old civil war.
But they also said it was unlikely Mr Obama would order strikes now and may not make any final decisions at the planned meeting.
Mr Johnson’s comments follow calls from MPs on both sides of the Commons for the establishment of a no-fly zone to end the air strikes on Aleppo.
“If Putin does to Aleppo what he did to Grozny, then they are going to flatten it.” Liberal Democrat foreign affairs spokesperson Tom Brake said his party had been calling for no-fly zones and air-drops in Syria for months.