Military parade in Kiev for Ukraine's independence day

Kiev, Ukraine (CNN) -- A military parade will roll through the capital of Kiev on Sunday as part of the celebrations of Ukraine's independence day.

The country declared its independence in 1991 from the Russian dominated Soviet Union during its dissolution.

But not everyone will be celebrating it. In eastern Ukraine, in territories held by pro-Russian rebels, there will be counter demonstrations by many who long for bygone Soviet area times.

Convoy back to Russia

A day earlier, a convoy of trucks that had crossed the border from Russia into eastern Ukraine without Kiev's authorization returned to Russia, international monitors said Saturday.

In total, 227 vehicles were sent into territories held by pro-Russian rebels on Friday, according to the Organization for Security and Co-operation in Europe, which has an observer mission at the checkpoint the convoy went through.

By Saturday afternoon, they had all returned to Russia after delivering aid to the city of Luhansk, a stronghold for the pro-Russia rebels that has been caught up in conflict.

Russia said the vehicles were on an essential humanitarian mission and that it was satisfied with the deliveries, but international powers condemned it as a violation of Ukraine's sovereignty.

Western outrage

Officials in Kiev referred to it as an invasion.

Amid the furor, German Chancellor Angela Merkel met in Kiev on Saturday with Ukrainian President Petro Poroshenko.

At a joint news conference, Merkel said she could not rule out further sanctions against Russia if no progress is made in resolving the situation in eastern Ukraine.

Poroshenko said the Russian convoy had 'violated every international law.'

But he also said he was committed to constitutional reforms and decentralization of power aimed at meeting the concerns of the Russian-speaking population in eastern Ukraine.

The Ukrainian President is due to meet with Russian President Vladimir Putin and EU representatives on Tuesday in Minsk, Belarus.

Red Cross did not monitorThe first trucks of a Russian aid convoy roll on the main road to Luhansk in eastern Ukraine on Friday, August 22. The head of Ukraine's security service called the convoy a 'direct invasion' under the guise of humanitarian aid since it entered the country without Red Cross monitors. Ukrainian government forces have been battling pro-Russian rebels near Ukraine's eastern border with Russia. The fighting has left more than 2,000 people dead since mid-April, according to estimates from U.N. officials.Photos: Crisis in Ukraine Kiev: Russian convoy an 'invasion' Ukrainian military tries to retake Donetsk

All the vehicles were supposed to be monitored by members of the International Committee of the Red Cross. However, the Red Cross said it wasn't accompanying them due to the 'volatile security situation' -- a reference to continued fighting between pro-Russia rebels and Ukrainian forces.

Ukraine's National Security and Defense Council has said that preliminary information indicated that many of the empty trucks were filled up with military equipment from arms factories that are now in rebel hands. Those weapons were then carried back over the border.

Since Soviet times, Russia's defense industry has relied heavily on the arms factories in eastern Ukraine.

'Humanitarian' aid or 'direct invasion'?Criticism of both sides

In a statement Saturday, OSCE chairman Didier Burkhalter deplored the failure to deliver the aid according to the agreements made between Russia and Ukraine.

Appealing to all sides to cooperate in helping civilians impacted by the fighting in Luhansk and Donetsk, he urged them 'to exercise maximum restraint and refrain from any actions which could contribute to the further escalation of the situation.'

But violence erupted Saturday night when shelling in Donetsk left three people dead and three others injured, according to the Donetsk mayor's office. Journalists on the scene said one of the three was a child. Bystanders claimed all were members of one family.

Donetsk: Photos of a besieged city draining of lifeRussian troops

There's also growing international concern over the apparent amassing of Russian troops at the border with Ukraine.

There were up to 18,000 such 'combat-ready' troops on Friday, according to U.S. estimates, a significant increase from previous public estimates by the Pentagon.

A U.S. official said the United States has believed for weeks that some Russian troops have crossed the border as part of the flow of military gear and weapons moving from Russia into Ukraine.

U.N. officials estimate that more than 2,000 people have died and nearly 5,000 have been wounded in eastern Ukraine since mid-April.

UEFA sanction Russia over Crimea

Journalist Victoria Butenko reported from Kiev and CNN's Laura Smith-Spark wrote and reported in London. CNN's Ben Brumfield wrote and reported from Atlanta. Diana Magnay, Greg Botelho and Radina Gigova contributed to this report.

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