While most of the victims were Dutch, there were 17 nationalities on board including Australians, Britons, Malaysians and Indonesians.
Ukrainian President Petro Poroshenko says Russian Federation must be held to account over the downing of Malaysia Airlines flight MH17, three years after the tragedy that killed 298 people.
MH17 crashed near the border of Russian Federation and Ukraine on July 17, 2014. Worldwide investigators have concluded that the Buk missile was sacked from Russia-backed rebel-controlled territory by a mobile launcher trucked in from Russian Federation and hastily returned.
In a statement, Mogherini said: "To ensure that those responsible for the downing of MH17 are held accountable and brought to justice, the criminal investigation needs the continuing support of the global community".
"It was a barefaced crime that could have been avoided if not for the Russian aggression, Russian system and Russian missile that came from Russian territory", Poroshenko said.
In addition to renewed calls for accountability, leaders also expressed their ongoing condolences.
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Both men declined further comment, with Barnier saying they would brief the media on Thursday after their teams have spent four days tackling a range of priority issues.
Funded by donations, the project was designed by artist Ronald A. Westerhuis and landscape architect Robbert de Koning after it was chosen out of three proposals by relatives in late 2015.
Each of the trees bears the name of one of the victims.
"A tree symbolizes "hope" and "future" in many cultures", the association for the victim's families said in a statement.
"Today, lighting the candles in memory, we bow our heads before 298 innocent victims of MH17 flight crash". And at the heart of the forest of 11 different tree varieties is a steel memorial shaped like an eye, turned upwards looking at the skies.
Sunflowers, which have been planted around the trees, will "radiate a golden glow" as well as recall the fields of sunflowers that cover fields in the area of eastern Ukraine where wreckage from flight MH17 was found.
On Sunday, the Australian foreign minister said that suspects may be tried in absentia, while earlier this month, the Dutch government announced that any trials will be held in the Netherlands.