Baghdad  - US President Barack Obama warned of difficult times ahead for Iraq on Tuesday, during a surprise visit at the end of his eight-day European tour.

The coming 18 months could be critical, said Obama, speaking to US troops at the Camp Victory US military base at Baghdad airport. Obama was greeted enthusiastically by several hundred soldiers.

US troops are due to begin withdrawing from Iraq in 2010, as Iraqi troops take over responsibility for security.

However, in recent weeks violence has picked up in the country,and shortly after Obama's meeting with the troops, al-Jazeera satellite channel reported an explosion outside a mosque in the Qadhimiya neighbourhood of Baghdad which killed at least 9 people.

On Monday seven bombs - six in Baghdad and one in Mosul - killed at least 42 people.

"Our role is to train Iraqis to take control of their own country so we can start bringing our folks home," Obama said.

Obama Tuesday described Iraq as "a growing democracy" and an "extraordinary achievement."

Speaking to soldiers, Obama praised their contribution and assured support beyond the end of the conflict.

"Michelle and myself are with you every day. We will support families (with) increases coming in my budget (and) commitment to veterans," he said.

"As long as I'm in the White House, you are going to get the support that you need," Obama added.

The president, who departed from Istanbul where he made an appeal for a new US relationship with the Muslim world, spoke by telephone with Iraqi President Jalal Talabani and Prime Minister Nuri al- Maliki, White House spokesman Robert Gibbs said.

Obama's helicopter transfer to the meeting with the two Iraqi leaders, which on security grounds was not pre-announced, was cancelled because of poor weather.

Gibbs went on to say that the reason the surprise visit was made was because President Obama wished to show his appreciation to the US troops serving in the country, and to consult with the Iraqi leadership.

Observers prior to Obama's arrival reported hectic activity in Prime Minister Nuri al-Maliki. The Voices of Iraq news agency reported the unannounced arrival in Baghdad of President of Iraqi Kurdistan Massoud Barzani and Kurdish Prime Minister Nerchivan Barzani.

Osama al-Najafi, a Sunni member of parliament with the Iraqi National List, welcomed Obama's visit, telling the German Press Agency dpa that "Obama's policy is based on openness to the Arab and Islamic world, seeking to change the United States' image and to rectify the grave mistakes (former US president George W) Bush and US forces committed in Iraq."

Obama arrived in Baghdad at 4:42 pm (1342 GMT) from Istanbul, where he said he was "deeply committed to rebuilding a relationship between the United States and the people of the Muslim world. One that is grounded in mutual interest and mutual respect."