Police in Istanbul detained more demonstrators on Tuesday when they tried to march towards Istanbul's symbolic main square in defiance of a May Day ban.

Turkish authorities declared Taksim Square off-limits to May Day celebrations, citing security concerns.

Roads leading to the square were blocked and police allowed only small groups of labour union representatives to lay wreaths at a monument there.

The demonstrators were detained as they tried to push their way into the square but were rounded up by riot police.

More than a dozen demonstrators were detained earlier on Tuesday.

Major trade unions were scheduled to mark the day with rallies at government-designated areas in Istanbul and Ankara.

Taksim has symbolic meaning for Turkey's labour movement after 34 people were killed there during a May Day event in 1977 when shots were fired into the crowd from a nearby building.