Mr Ahtisaari was praised for more than three decades of peace work
Northern Ireland politicians have been paying tribute to Finnish diplomat Martti Ahtisaari, who has won the Nobel Peace Prize.
One of Mr Ahtisaari's roles during his long career in peace mediation was as an IRA weapons inspector in 2001.
Sinn Féin President Gerry Adams said he "played a positive and constructive role in the Irish peace process".
SDLP leader Mark Durkan said Mr Ahtisaari's "credibility was a help at a time of problem in our own process".
Irish President Mary McAleese said the prize was "a fitting recognition of the outstanding work of this quiet, unassuming champion of peace over many years in seeking to bring to an end several difficult and intractable conflicts".
She added: "His work with Cyril Ramaphosa in verifying that IRA arms were put beyond use has rightly earned him the gratitude of the Irish people."