Kerry to meet Zarif for latest US-Iran nuclear talks

US secretary of state John Kerry and Iranian foreign minister Mohammad Javad Zarif are to meet this weekend in Switzerland as efforts intensify to reach a comprehensive nuclear accord.

The top diplomats will hold talks on Saturday in Geneva.

State Department spokesman Jeff Rathke said on Wednesday that the goal is to make progress toward an agreement by an end-of-June deadline.

European and Iranian officials have suggested the talks may require more time, undersecretary Wendy Sherman, will leave when the negotiations with Iran are finished.

Sherman has led much of the technical discussion in Europe with Iranian officials over the last two years. During her tenure the US and Iran reached an interim agreement in November 2013 and a framework pact in April.

Kerry called Sherman a "critical" member of his team, hailing her "tenacity and skill".

Kerry leaves Washington on Thursday for Nigeria, where he'll attend Muhammadu Buhari's presidential inauguration.

From Geneva, Kerry will head to Madrid to meet with Spain's king and prime minister. Later, Kerry will attend a conference in Paris on fighting the Islamic State group.