Negotiation is a central process in an agent society where autonomous agents have to cooperate in order to resolve conflicting interests and yet compete to divide limited resources. A direct dialogical exchange of information between agents usually leads to competitive forms of negotiation where the most powerful agents win. Alternatively, an intelligent mediated interaction may better achieve the goal of reaching a common agreement and supporting cooperative negotiation. In both cases argumentation is the reference framework to rationally manage conflicting knowledge or objectives, a framework which provides the fundamental abstraction "argument" to exchange pieces of information. In this paper we present a novel conceptual framework for negotiation dialogues using argumentation between autonomous software agents which enables their dialogues to be automated. The framework, called SANA (Supporting Artifacts for Negotiation with Argumentation), incorporates intelligent components able to assist the agent participants to reach agreement by inferring mutually-acceptable proposals. The framework also permits agents to engage in negotiation dialogues with each other, generating and exchanging proposed deals and arguments for and against these proposals. Acceptability of proposals is then assessed in terms of an agreed argumentation framework semantics. We present the architecture of our framework, along with the syntax, and outline denotational semantics of an associated agent interaction protocol, called SANAP.