Some 280 trucks struck out from the Moscow area on Tuesday morning, heading for eastern Ukraine, according to Russian state media. The convoy was reportedly carrying 2,000 tons of humanitarian aid.

The initiative, which is in cooperation with the International Committee of the Red Cross (ICRC), had been announced the previous day by Russian Foreign Minister Sergei Lavrov. Ukrainian President Petro Poroshenko later confirmed that Kyiv welcomed the assistance from Moscow.

According to Russian media on Tuesday, the roughly 1,000-kilometer (620-mile) journey from Moscow to eastern Ukraine would take two to three days. Representatives from the ICRC are to meet the convoy at the Ukrainian border.

Once inside Ukraine, the convoy will be escorted by representatives from the Organization for Security and Cooperation in Europe (OSCE), according to Reuters new agency.

Fighting between separatist rebels and the Ukrainian government has left more than 1,100 people dead, according to UN agencies.

Hundreds of thousands of civilians have fled the embattled region. Those who have remained behind are believed to be without power, water and medical supplies.

Convoy just a cover-up?

Western leaders have expressed concern about the conyov's contents considering the build-up of Russian troops close to the Ukrainian border - roughly 45,000 according to estimates from NATO - and Russia's backing of the separatists.

"We must be extremely careful because this could be a cover for the Russians to install themselves near Luhansk and Donetsk and put us before a done deed," French Foreign Minister Laurent Fabius told France Info radio on Tuesday.

"This [convoy] is only possible, only justifiable, if the Red Cross authorizes it," he added.

On Monday, NATO chief Anders Fogh Rasmussen accused Russia of "developing the narrative" for "illegal military operations" in Ukraine under the guise of humanitarianism.

US vows justice in MH17 probe

Russia's alleged involvement in the downing of Malaysian Airlines flight MH17 has further strained diplomatic relations with Western leaders. They accuse separatist rebels of shooting down the commercial airliner with technology provided by the Russian military. The incident has led to both sides levying sanctions on one another.

Speaking to reporters in Australia on Tuesday, US Secretary of State John Kerry demanded justice for the "unconscionable crime."

"It is no mystery where [this weapon] came from and where the weapons have come from," he said, adding that a full investigation would be needed to "legitimize whatever steps we are to take down the road."

All 298 people on board MH17 were killed. Most of the passengers were Dutch nationals. Australia lost 38 of its own in the disaster.

kms/ng (AP, AFP, Reuters, dpa)