BEIRUT (Reuters) - A decision by a Kurdish opposition group to take up arms against Iranian authorities has senior officials in Tehran worrying that Saudi Arabia is seeking to undermine its stability in a deepening of their regional rivalry.

Riyadh denies the charge. But tension between the two countries is surging, with Saudi Arabia and Iran supporting opposite sides in wars in Syria and Yemen and rival political parties in Iraq and Lebanon. The contest has largely hewed along sectarian lines as mainly Shi'ite Iran and Saudi Arabia, a predominantly Sunni country, vie for influence.