PARIS 

At least six riot police officers were injured Monday after clashes erupted on the sidelines of May Day demonstrations in the French capital Paris and in Loiret, in north-central France.

"Masked individuals threw objects and Molotov cocktails at police," who responded by firing teargas, Interior Minister Matthias Fekl said in a statement.

He said two police officers were critically wounded, one in his hand, the other with burns on his face.

The occasional clashes broke out between masked youths and police during the rally organized by French hard-left trade unions on its way to Place de la Nation in Paris. 

At least four people were arrested in Paris, according to police.

The Interior Ministry estimates that some 142,000 people were demonstrating across the country.