BAGHDAD (REUTERS) - US Vice President Joe Biden met Iraqi Prime Minister Haider al-Abadi and other top officials in an unannounced visit to Baghdad on Thursday to show support for the government as it seeks to build on wins against ISIS amid a distracting political crisis.

It is the first visit for Biden, the White House's point person on Iraq, since US forces withdrew in 2011 after nearly nine years of occupation. He is the third and highest-level US official to visit the country this month.

The Islamic State in Iraq and Syria, also known as ISIS and ISIL, seized large portions of Iraq and neighbouring Syria in 2014. Iraqi forces have won back some territory, such as the western city of Ramadi, but often after long battles that have left the areas destroyed.

Biden's trip, several months in planning, is a sign of the progress Washington believes Iraqi forces have made in beating back the militants over the past year.

"This is a good indication of the United States' continued support for Prime Minister Abadi's efforts to unify the nation of Iraq to confront ISIL," White House spokesman Josh Earnest said.

The vice president has close relationships with Iraqi leaders and speaks with them about every 10 days. Still,"there's no substitute for being able to sit down face-to-face,"a US official said.

Biden, a long time US senator before becoming vice president, said he had been to Iraq almost 30 times during his career.

On Thursday he discussed "progress" in the fight against ISIS with Abadi and then Parliament Speaker Salim al-Jabouri, including plans to retake the northern city of Mosul.

"It's real. It's serious. It's committed," he told reporters afterwards.

Iraqi officials say they will retake Mosul this year but, in private, many question whether that is possible. Biden hopes some progress can be made before the extreme summer heat, a senior administration official said.

His trip serves to counter a "misperception in the region"that Iran, which backs powerful Shi'ite Muslim militias fighting Islamic State in Iraq, has undue influence in the nation, the official added.

But it comes at a turbulent time in Iraqi politics. Abadi has faced resistance to a government overhaul aimed at tackling corruption. He won lawmakers' approval to replace a handful of ministers on Tuesday after weeks of delays and disruptions from dissenting MPs.

The political battle has also sparked populist protests that have forced the government to bring back troops from the front lines to secure the capital.

US officials have expressed concern that the unrest could distract from the war effort. Secretary of State John Kerry and Defence Secretary Ash Carter visited Baghdad earlier this month to show their support.

"It's been a pretty all-consuming political affair," a senior U.S. official told reporters, noting recent signs of a"calmer trajectory" in the drama.

President Barack Obama has said he has seen "momentum" in the efforts of a U.S.-led coalition fighting Islamic State, and recently authorized more US forces to go to Iraq and Syria to help train and assist local fighters.

Their goal is to help Iraqi and Kurdish forces retake Mosul by the end of the year. The United States has already redeployed several thousand troops to Iraq to help defeat Islamic State.

The White House is concerned that not enough is being spent to rebuild parts of Iraq devastated by the fight, a deficit made worse by the low price of oil, Iraq's main revenue source.

The United Nations is urgently seeking US$400 million (S$538.94 million) from Washington and its allies for reconstruction, while Obama asked Gulf Arab leaders to assist during a visit to Riyadh last week.

He also discussed the issue with European leaders in London and Hanover, Germany, and told reporters Iraqi reconstruction would be a topic for the G7 meeting in Japan next month and for NATO.

Biden, whose late son Beau spent a year in Iraq with the army, later spoke with US troops and embassy workers. He showed them a daily tally of the number of US troops serving, killed, and injured in the line of duty which he carries in his front suit pocket.

"The history of this region is a nightmare from which everyone is constantly trying to awake," he said, adapting a line from Irish novelist James Joyce.