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By Denis Dumo

JUBA Oct 3 (Reuters) - South Sudanese rebels said on Saturday government troops had attacked their positions over the last three days, casting further doubt on a fragile peace agreement in the world's youngest country.

No one was immediately available to comment from the government - but both sides have regularly accused the other of breaking the ceasefire ratified by parliament last month under pressure from the United Nations, regional and world powers.

"For the last three days we have received a report of the government forces on the offensive, attacking our positions in Unity state," rebel spokesman James Gatdet Dak said, referring to an oil-producing region on the northern border with Sudan.

"The intention was actually for them to control the areas we have been holding for a number of months, and this is a clear violation of the permanent peace agreement."

South Sudan split away from Sudan in 2011 under the terms of a peace deal that ended decades of north-south civil war.

But a political row between President Salva Kiir and his sacked deputy Riek Machar descended into fighting inside the country in Dec. 2013, often along ethnic faultlines.

The fragile deal, which followed a series of failed ceasefires, came under further pressure when Kiir announced late on Friday he had increased the number of administrative states to 28 from 10, an action the rebels say was taken unilaterally.

In his decree, Kiir said it would move more power into the regions and create a more federal government.

"This presidential decree is a violation of the peace agreement and is a clear message to the world that president Kiir is not committed to peace," Machar said in a statement. (Writing by George Obulutsa; Editing by Andrew Heavens)