Mr Doherty was addressing a conference in London
A senior Sinn Fein member has said the "denial of the Irish people's right to self determination" remains a core outstanding issue of the peace process.
West Tyrone MP Pat Doherty was speaking at a conference organised by the party in London to discuss Irish unity.
He said the Good Friday Agreement was "an accommodation, not a settlement".
"Sinn Fein seeks to build on this by working in partnership with others of like mind to build political support for Irish reunification," he added.
Mr Doherty said the peace process had delivered an end to war.
"However, resolving the many complexities resulting from centuries of occupation and partition was never going to be easy.
"And for Irish republicans, the cause still persists - the British government's claim of jurisdiction over part of our country," he said.
He said the cause of Irish unity should be put on the British and international political agendas.
"We just have to believe and work hard and the impossible can be achieved," he said.