Marseille move for Diarra and Nkoulou
Recruiting the 29-year-old, who has 34 caps, was a priority for Marseille coach Didier Deschamps as he looks to shore up his midfield with Lucho Gonzalez poised to leave.
Monaco defender Nicolas Nkoulou earlier signed for Marseille on a four-year deal following his side's relegation.
His new club, who lost the French title to Lille last season, needed cover after Nigeira international Taye Taiwo left for AC Milan and Argentine Gabriel Heinze also departed.
Deschamps' side have already recruited Morgan Amalfitano and Jeremy Morel from Lorient during the close season.