UN Secretary-General Ban Ki-moon arrived in Baghdad on March 30 for talks with Prime Minister Haidar al-Abadi and other senior officials.
Ban's spokesperson said on Twitter that the UN chief would "convey UN support" for the people and government of Iraq "in these challenging times."
Reuters news agency quoted an unnamed UN official as saying Ban would "meet Iraqi leaders to discuss the political and security developments in the country."
Iraqi forces are fighting Islamic State militants who swept across much of the country's north and west last year.
Government forces are aided by air strikes conducted by a U.S.-led coalition.
Tikrit, the hometown of late former dictator Saddam Hussein, has been a major focus of the military campaign against the militants for weeks.
Ban attended an Arab League summit over the weekend in Egypt.
With reporting by AFP and Reuters