Twitter is holding to a \"principled\" policy on national security data requests and will \"push back\" in some cases to protect the privacy of its users, its chief executive said Wednesday. Dick Costolo, appearing at a forum at the Brookings Institution in Washington, declined to comment on whether Twitter had specific requests under the vast data-gathering program called PRISM made public this month. But he said the popular messaging service maintains its policy of allowing users to be informed of any requests from authorities, both in the United States and abroad. \"We\'ve been very clear about having articulated a very principled policy around access to user data,\" he said. \"When we receive a valid, legal request in the countries in which we operate we will abide by the rule of law.\" He added that for \"other requests that may be more broad in scope and not specific legal requests that don\'t meet our principle... we will push back on.\" Twitter was not among the nine Internet firms cited in documents for providing access to the secretive National Security Agency, which seeks to identify potential terrorist threats from abroad. Costolo steered clear of questions on why Twitter was absent from the list, which includes Google, Yahoo!, Facebook, Microsoft and Apple. But he noted that Twitter has gone to court in certain cases to fight \"gag\" orders and to allow users to be in informed of how their own data is used. \"We feel that our users have a right to know when their information is being requested,\" he said. \"This is not just something we deal with in the US, it\'s something we deal with in all the countries (where) we operate.\" Costolo also defended the messaging platform in the face of criticism from Turkish Prime Minister Recep Tayyip Erdogan, who branded Twitter as a \"troublemaker\" inciting protests against his rule. \"The beauty of having this open public platform that allows everybody around you to see and hear what you think is that... that it\'s this public town square. That\'s what it is. We don\'t editorialize what\'s on it,\" he said. \"We don\'t say, \'If you believe this you can\'t use our platform.\' You can use our platform to say what you believe... The platform itself doesn\'t have any perspective on this. It\'s a vehicle for people to give their perspective.\"