A protester falls during clashes with police in Besiktas neighbourhood of Istanbul, Turkey, May 1, 2015. Turkish police used water cannon and tear gas on hundreds of stone-throwing protesters on Friday, a Reuters reporter at the scene said, after the demonstrators attempted to defy a ban and march on Taksim Square in central Istanbul. REUTERS/Murad Sezer 

A masked protester runs away from a water cannon's jet during clashes with police in Okmeydani neighbourhood in Istanbul, Turkey, May 1, 2015. Istanbul went into a security lockdown on Friday as thousands of police manned barricades and closed streets to stop May Day rallies at Taksim Square, a symbolic point for protests. REUTERS/Kemal Aslan TPX IMAGES OF THE DAY 

A protester lies in front of policemen during clashes with police in Besiktas neighbourhood of Istanbul, Turkey, May 1, 2015. Turkish police used water cannon and tear gas on hundreds of stone-throwing protesters on Friday, a Reuters reporter at the scene said, after the demonstrators attempted to defy a ban and march on Taksim Square in central Istanbul. REUTERS/Murad Sezer

Protesters fire firecrackers as they clash with police in Okmeydani neighbourhood of Istanbul, Turkey, May 1, 2015. Turkish police used water cannon and tear gas on hundreds of stone-throwing protesters on Friday, a Reuters reporter at the scene said, after the demonstrators attempted to defy a ban and march on Taksim Square in central Istanbul. REUTERS/Umit Bektas 

A protester uses a catapult during clashes with police in Okmeydani neighborhood of Istanbul, Turkey, May 1, 2015. Istanbul went into a security lockdown on Friday as thousands of police manned barricades and closed streets to stop May Day rallies at Taksim Square, a symbolic point for protests. REUTERS/Huseyin Aldemir

A masked protester walks during clashes with police in Okmeydani neighbourhood in Istanbul, Turkey, May 1, 2015. Istanbul went into a security lockdown on Friday as thousands of police manned barricades and closed streets to stop May Day rallies at Taksim Square, a symbolic point for protests. REUTERS/Kemal Aslan TPX IMAGES OF THE DAY 

A police officer in a gas mask looks at people watching from inside a street shop during clashes in Okmeydani neighbourhood in Istanbul, Turkey, May 1, 2015. Istanbul went into a security lockdown on Friday as thousands of police manned barricades and closed streets to stop May Day rallies at Taksim Square, a symbolic point for protests. REUTERS/Kemal Aslan TPX IMAGES OF THE DAY 

Two protesters prepare Molotov cocktails during clashes with police in Okmeydani neighborhood in Istanbul, Turkey, May 1, 2015. Turkish police fired tear gas and water cannon at hundreds of stone-throwing May Day protesters on Friday, after they defied a ban and tried to march on Istanbul's Taksim Square. REUTERS/Huseyin Aldemir

A protester throws a Molotov cocktail during clashes with police in Okmeydani neighborhood in Istanbul, Turkey, May 1, 2015. Istanbul went into a security lockdown on Friday as thousands of police manned barricades and closed streets to stop May Day rallies at Taksim Square, a symbolic point for protests.REUTERS/Kemal Aslan 

Protesters take cover behind a banner during clashes with police in Besiktas neighbourhood of Istanbul, Turkey, May 1, 2015. Turkish police used water cannon and tear gas on hundreds of stone-throwing protesters on Friday, a Reuters reporter at the scene said, after the demonstrators attempted to defy a ban and march on Taksim Square in central Istanbul. REUTERS/Murad Sezer 

Police officers in gas masks detain a protester during clashes in Okmeydani neighbourhood in Istanbul, Turkey, May 1, 2015. Istanbul went into a security lockdown on Friday as thousands of police manned barricades and closed streets to stop May Day rallies at Taksim Square, a symbolic point for protests. REUTERS/Kemal Aslan 

A protester looks on during clashes with police in Okmeydani neighborhood in Istanbul, Turkey, May 1, 2015. Istanbul went into a security lockdown on Friday as thousands of police manned barricades and closed streets to stop May Day rallies at Taksim Square, a symbolic point for protests. REUTERS/Huseyin Aldemir

Plain clothes policemen detain a protester during clashes in Besiktas neighbourhood of Istanbul, Turkey, May 1, 2015. Turkish police used water cannon and tear gas on hundreds of stone-throwing protesters on Friday, a Reuters reporter at the scene said, after the demonstrators attempted to defy a ban and march on Taksim Square in central Istanbul. REUTERS/Murad Sezer 

REFILE-CORRECTING LOCATION Protesters take cover as they clash with police in Okmeydani neighborhood of Istanbul, Turkey, May 1, 2015. Istanbul went into a security lockdown on Friday as thousands of police manned barricades and closed streets to stop May Day rallies at Taksim Square, a symbolic point for protests. REUTERS/Huseyin Aldemir

Policemen block a street to prevent people from gathering for May Day demonstrations near Taksim Square in Istanbul, Turkey, May 1, 2015. Istanbul went into a security lockdown on Friday as thousands of Turkish police manned barricades and closed off streets to traffic to stop May Day rallies at the central Taksim Square, a symbolic point for anti-government protests. REUTERS/Umit Bektas 

A protester plays with a ball during clashes with police in Okmeydani neighborhood in Istanbul, Turkey, May 1, 2015. Istanbul went into a security lockdown on Friday as thousands of police manned barricades and closed streets to stop May Day rallies at Taksim Square, a symbolic point for protests.REUTERS/Kemal Aslan 

Protesters shout slogans as they march with banners in Besiktas neighbourhood of Istanbul, Turkey, May 1, 2015. Turkish police used water cannon and tear gas on hundreds of stone-throwing protesters on Friday, a Reuters reporter at the scene said, after the demonstrators attempted to defy a ban and march on Taksim Square in central Istanbul. REUTERS/Murad Sezer 

REFILE-CORRECTING LOCATION A protester is detained by policemen during clashes in Okmeydani neighborhood of Istanbul, Turkey, May 1, 2015. Istanbul went into a security lockdown on Friday as thousands of police manned barricades and closed streets to stop May Day rallies at Taksim Square, a symbolic point for protests. REUTERS/Huseyin Aldemir

A protester runs during clashes with police in Okmeydani neighborhood in Istanbul, Turkey, May 1, 2015. Istanbul went into a security lockdown on Friday as thousands of police manned barricades and closed streets to stop May Day rallies at Taksim Square, a symbolic point for protests.REUTERS/Kemal Aslan 

Vendors watch the street from their shop window as policemen block streets to prevent people from gathering for May Day demonstrations near Taksim Square in Istanbul, Turkey, May 1, 2015. Istanbul went into a security lockdown on Friday as thousands of Turkish police manned barricades and closed off streets to traffic to stop May Day rallies at the central Taksim Square, a symbolic point for anti-government protests. REUTERS/Umit Bektas