"No doubt you all know that we are targeted in our safety and security. That is why we have to take responsibility," he said, addressing the opening session of a meeting of the six-member Gulf Cooperation Council (GCC) in the Saudi capital Riyadh.
Saudi Arabia, the world's top oil exporter, has accused Iran of supporting an alleged plot uncovered in October by the United States to assassinate the Saudi Ambassador in Washington.
Iran has denied the charges and Iranian Intelligence Minister Heydar Moslehi visited Riyadh last week in an effort to cool tensions.
King Abdullah also suggested that the GCC needed to adapt to new circumstances in the Middle East following the popular uprisings that swept some Arab countries earlier this year.
"We learnt from history and experience not to stand still when faced with our reality," HRM said.
"Whoever does that will end up at the back of the caravan trail and will be lost... That is something we will not accept for the sake of our countries, our people, our stability and our security. That is why I ask of you today to move beyond the stage of cooperation and into the stage of unity in a single entity," he added.