US Secretary of State Hillary Clinton has arrived in Dublin for an international security conference.
Foreign Secretary William Hague is also among the 50 dignitaries attending the Organisation for Security and Co-operation in Europe (OSCE) meeting.
She is due to travel to Belfast on Friday to discuss the peace process and economic opportunities.
Her visit may be one of her last foreign engagements.
Mrs Clinton's term ends in December and she has said she does not want a second term.
She visited Northern Ireland three times with her husband, former US president Bill Clinton during his time in office from 1993 and 2001.
The most memorable was in 1995 when they turned on the Christmas lights in Belfast just a year after the first IRA ceasefire.
Mrs Clinton has also come to Northern Ireland without her husband.
In 1999 she gave a keynote address to a women's conference and in October 1997 gave the Tip O'Neill Memorial lecture at the University of Ulster's Magee campus in Londonderry.