Greece has been left without national rail, island ferry and other transport services for a day as unions hold strikes and rallies to celebrate May Day.
Hundreds of people gathered in central Athens Wednesday for three separate rallies and marches to parliament organised by rival unions and left-wing groups.
The Greek capital was left without public bus, trolley bus and urban rail services all day due to a 24-hour transport union strike, although the city's metro trains were running most of the day.
The national train and island ferry services are set to resume Thursday.
Russian authorities say that about 100,000 people are taking part in a May Day rally in central Moscow.
Moscow police said on Wednesday that the rally organised by Kremlin-friendly trade unions on Red Square attracted around 100,000 people.
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Over the years, the May Day in Russia has transformed from the occasion for rallies for workers' rights to an official event carefully orchestrated by Kremlin-controlled groups.
Opposition activists, however, often try to use the May Day to promote their agenda.
The respected activists' group OVD-Info which compiles police reports on detentions of political activists said that six political activists have been detained in Moscow before the morning rallies.
Separately, in the remote Petropavlovsk-Kamchatsky in Russia's Far East, police have detained at least 10 people who showed up at the local May Day rally wearing yellow vests in an apparent nod to the protest movement in France.
Turkish police detained May Day demonstrators who tried to march toward Istanbul's symbolic main square in defiance of a ban.
Turkey declared Taksim Square off-limits to May Day celebrations citing security concerns. Roads leading to the square were blocked Wednesday and police allowed only small groups of labor union representatives to lay wreaths at a monument.
Still, small groups chanting "May Day is Taksim and it cannot be banned," attempted to break the blockade. The official Anadolu news agency said more than two dozen were detained.
Trade unions and political parties will mark the day with rallies at government-designated areas in Istanbul and the capital, Ankara.
Taksim holds symbolic value for Turkey's labor movement. In 1977, 34 people were killed there during a May Day event when shots were fired into the crowd from a nearby building.
Ahead of a May Day rally in over a dozen German cities, Germany's biggest trade unions are urging voters to participate in this month's European elections and reject nationalism and right-wing populism.
The DGB, a confederation of unions with almost 6 million members, said Wednesday that the European Union has helped ensure peace on the continent for decades and brought significant benefits to millions, from paid holidays to maternity protection.
The unions called for ambitious EU-wide investments to boost employment and growth, saying "people must feel that the EU improves their lives in a lasting and tangible way."
The unions warned that the political and economic turmoil in Britain following its vote to leave the European Union nationalism "shows what happens if those who stoke fear but have no plan for the future gain the upper hand."