The UK's Iraq inquiry has visited the cities of Baghdad and Basra as part of its fact-finding mission.
Members of the panel held talks with Deputy Foreign Minister Labeed Abbawi and former Prime Minister Ayad Allawi, as well as leading Iraqi officials.
Its report, into the run-up to the 2003 invasion of Iraq and its aftermath, is due to be published early next year.
Inquiry chairman Sir John Chilcot promised that the panel would "seek to fill" any "gaps in the evidence".
Its public hearings in central London, which numbered former Prime Ministers Tony Blair and Gordon Brown among the witnesses, concluded in July.
But Sir John said there could be more sessions, if it was judged that the information gathered so far was inadequate.
From 26 September to 1 October, four of the five-member inquiry panel visited Iraq for private discussions with leading politicians and officials.
As well as Mr Abbawi and Mr Allawi, these included Iraq's planning minister Ali Baban and Ahmed Chalabi, leader of the Iraqi National Congress Party.
United Nations, European Union and World Bank officials also held discussions with the panel.
Sir John said: "Since the end of the public hearings in July, we have heard from many individuals; from British service personnel who served in Iraq, to Iraqi politicians and civilians living and working in the country today.
"All those meetings have been immeasurably helpful to the committee, and we are grateful to those who have hosted us and those who have taken the time to meet us to share their insights and experiences."
He added: "As I have said before, if there are gaps in the evidence we will seek to fill them, including seeking further written evidence or potentially holding a small number of further public hearings either with new witnesses or with those from whom we have heard before.
"Writing the report is an immense task but our objective remains to publish the report in early 2011."
In September, the inquiry also held private talks with Matthew Rycroft, Mr Blair's former private secretary dealing with foreign affairs, and Sir Nigel Sheinwald, the UK ambassador to the US who is a former foreign policy adviser to Mr Blair.
The panel is looking specifically at the UK's role in planning for the war and in its aftermath, including aid efforts and the economic reconstruction of Iraq.