(Adds more quotes by al-Jubeir, background) BERLIN, Feb 19 (Reuters) - Moderate Syrian rebels should be supplied with surface-to-air missiles to defend against air strikes, Germany weekly Der Spiegel quoted Saudi Foreign minister Adel al-Jubeir as saying. The rebels are under attack from both the Syrian air force and Russian strikes. Al-Jubeir repeated his calls for Syrian president Bashar al-Assad to step down in order to enable a political solution to the five-year-long war.