The Philippine supreme court has ruled that a deal giving Muslim separatists control over about 700 towns and villages on the southern Mindanao island was illegal.

The government had already effectively shelved the deal after the Moro Islamic Liberation Front (MILF) had reacted to an earlier court injunction by launching a series of attacks.

The raids on dozens of town and villages left at least 37 people dead.

Gleo Guerra, a spokewoman for the Philippines supreme court, said on Tuesday that eight of 15 justices had voted to declare the deal unconstitutional.

The Memorandum of Agreement on Ancestral Domain was to have paved the way for a final political settlement with the MILF, which has been fighting for autonomy in the south of the country since 1978.

But the court had blocked the signing of the deal on August 4 after Christian politicians claimed it violated the constitution and would lead to the country being split. 

Gloria Arroyo, the president, has sent additional troops to Mindanao and said peace talks will resume only if the separatists disarm and the leaders responsible for the renewed attacks surrender.