A tense debate in the Mexican Senate descended into a brawl between two of the chamber's most senior politicians on Wednesday.

Senator Alejandro Moreno, of the opposition Institutional Revolutionary Party (PRI), grabbed the president of the Senate, Gerardo Fernández Noroña, demanding to be allowed to speak.

After some pushing and shoving, Moreno threw punches and a photographer who stepped in was injured.

Tempers had already been running high throughout the debate about the presence of armed forces from other countries on Mexican soil.

But it was not until after the national anthem had been sung that Senator Moreno, angry at not having been allowed to speak during the debate, physically clashed with Fernández Noroña.

The Senate leader said he would call an emergency session to propose expelling Mr Moreno and three other opposition lawmakers who joined in the fray.