Systems management is the starting place.  When interpersonal conflict rears its ugly head, as manager ask yourself;

• Is the purpose of the team, and its connection to the organisation as a whole, clearly understood by all team members?
• Are employees clear on their individual contribution (i.e. role clarity) to the team?
• Is the team, and individuals within the team, adequately resourced and supported to undertake their responsibilities?
• Are employees given frequent and timely feedback; both affirming and corrective feedback?  Contrary to a popular perception, high performers require as much feedback as anyone.  Indeed, there is an insightful saying that “Feedback is the breakfast of champions”.  Imagine how difficult it would be for an Olympic athlete to improve if they were never given their performance times for events or their coaches never highlighted poor
  technique!
• Do employees have a “code of behaviour” to which they are held accountable?
• How does my behaviour as Manager reflect appropriate standards of behaviour?

A strong system will eliminate the vast majority of interpersonal problems in organisations, because the performance benchmarks and behavioural expectations are clear.  A strong system will also ensure that the consequences of not meeting expectations are well understood by employees and management.  Furthermore, a strong system will show commitment to applying consequences when expectations are not met because of individual dysfunction.

Managers - how does your system “stack up”?  How does your behaviour rate compared against a code of behaviour?  If you can respond positively, in good conscience, to both these questions and an employee continues to undermine team cohesion and productivity, you must commit to an educative or disciplinary process with the employee.