U.N.-Arab League envoy to Syria is winding up a days-long visit to Damascus with a call to both the Syrian government and the opposition to attend a planned peace conference in Geneva.

But Lakhdar Brahimi acknowledged that the conference, which the U.S. hopes will be held later this month, will not take place if the Syrian opposition refuses to take part.

Syrian opposition groups are split on whether to attend and the conditions for taking part.

Brahimi's plea comes just hours after officials said Israeli warplanes had attacked a shipment of Russian missiles inside a Syrian government stronghold — a development that threatened to add another volatile layer to regional tensions from the Syrian civil war.

Syrian officials and state media have not commented on the reports.