Clinton condemns 'cowardly' killing
US secretary of state Hillary Clinton has branded the killing of prison officer David Black as "cowardly".
She strongly condemned the murder as senseless and applauded the efforts of police to bring the perpetrators to justice.
"There is no justification for this outrageous and cowardly act," she said.
"I offer my sincere condolences to the family, friends and colleagues of officer Black, who had a long and distinguished record of service.
"The United States remains resolute in support of the people of Northern Ireland, who have condemned violence and embraced the path to peace and reconciliation."
Mrs Clinton and former president Bill Clinton have supported the Northern Ireland peace process since the 1990s.
Three men have been arrested by police investigating the shooting.