With the increasing penetration of distributed renewable energy, peer-to-peer (P2P) transactions among small scale consumers become possible. However, it remains challenging to maintain the operational security of distribution networks in P2P transactions. This paper proposes a novel integrated transaction and operation model to realize P2P transactions while ensuring the security constraints of distribution network simultaneously. The Vickrey-Clarke-Groves mechanism is used to solve the conflict between interests of prosumers in the P2P transactions and the operational requirements of distribution network. A zero-sum P2P settlement method is designed to quantify the expense among prosumers indicating their contributions to the safety operation of distribution network by controlling the flexible demand. A distributed algorithm based on sharing form alternating direction method of multipliers is developed for the P2P trading problem to derive transaction solutions of prosumers binding the power injection limits of connected buses. Numerical case studies based on IEEE 13-bus distribution network verify the effectiveness of the proposed model in motivating energy trading among prosumers against operational security violations of the distribution network and reducing the entire energy usage cost.