The first of a detachment of Ukrainian troops pledged to assist efforts to restore order in Iraq left Kiev on Thursday.
In total, 1,600 Ukrainian soldiers have been pledged to help in Iraq
An Orthodox priest blessed the 70 soldiers before they boarded an Ilyushin Il-76 plane at Borispil Airport, watched by family, friends, senior officials and around 800 military colleagues.
Ukraine, eager to rebuild US relations strained by accusations early this year that Kiev had supplied an air defence system to Iraq, has promised at least 1,600 soldiers to help patrol in Iraq.
But mounting American casualties in Iraq mean public support for such a mission is low.
And the mission has been tarnished by the revelation that two senior generals due to have joined it have been dismissed.
Defence Minister Yevhen Marchuk said military armaments chief Oleksandr Stetsenko and rear services commando Viktor Kolotov had lost their jobs because of their "poor preparation" of troops.
Correspondents say this is a clear indication of the strain the mission has put on Ukraine's chronically under-funded forces.
The Ukrainian departure came as Serbia's prime minister ruled out sending troops to join the US-led international division in Iraq.
Zoran Zivkovic said joining United Nations peacekeeping missions would be a good way for Serbia's military - accused of some of the worst atrocities of the Balkan wars - to repair its reputation.
However, he said, Serbian law forbade participation by the military in operations not run by the UN.
In total, 345 soldiers are set to arrive in a Kuwaiti training camp on Thursday. They are scheduled to reach their base in the town of Kut in central southern Iraq on Monday or Tuesday, the Defence Ministry said.
They are set to join a 9,000-strong Polish-led stabilisation force that will patrol a region between Baghdad and the southern port of Basra.
They are charged with guarding key highways and Iraqi army munitions depots, and delivering humanitarian aid in the Shia Muslim-dominated area.
Ukraine already has in the region 448 soldiers of the chemical, nuclear and biological warfare battalion sent to the Gulf during the US-led invasion.
Saying goodbye to the soldiers, Defence Minister Yevhen Marchuk told them they would have to be "vigilant and very professional to ensure [their] security and that of the local population".
"Participation in rebuilding Iraq corresponds to our national interests," he said.
"Ukraine is a major European country and it cannot stand aloof from international developments," he added.
However, Ukraine's participation in the campaign is facing strong opposition domestically. Critics say a recent attack on Polish peacekeepers has highlighted the dangers the Ukrainian contingent will face.
Correspondents say the contribution of troops has gone a long way towards repairing relations with the US, which nose-dived last year after Washington accused Kiev of supplying the sophisticated Kolchuga aircraft detection system to Baghdad in breach of international sanctions.
Ukraine denied the charges, which were based on wiretapped records made by President Leonid Kuchma's fugitive former bodyguard and authenticated in the US.