Ethiopia's Renaissance Dam and the diversion of the Blue Nile is a declaration of war on Egypt, Sheikh Abdel-Akher Hammad of Al-Gamaa Al-Islamiya said on Wednesday.
On Tuesday, Ethiopia began diverting the course of the Blue Nile, one of the Nile River’s two major tributaries, as part of its project to build a dam for electricity production.
Speaking on Al-Arabiya satellite channel, Hammad claimed the move would reduce Egypt's water supply and damage national security.
"If such a war is forged against us, we are ready to fight and we will embark on it with all our strength to defend our honour," asserted Hammad.
Diplomatic negotiations should be the first step, he added.
Hammad went on to say the crisis should have been dealt with by the Mubarak regime.
The Blue Nile provides Egypt with the lion's share of its annual 55 billion cubic metres of river water.
According to the state-run National Planning Institute, Egypt will need an additional 21 billion cubic metres of water per year by 2050 – on top of its current quota of 55 billion metres – to meet the needs of a projected population of 150 million.