KATHMANDU, Nov 18 (Reuters) - Nepal's former Maoist rebels launched fresh protests against the monarchy on Sunday with thousands of their supporters parading in anti-king rallies, demanding an immediate declaration of a republic.

Sunday's demonstrations were the first by the Maoists since the interim parliament passed two non-binding resolutions this month urging the government to prepare for a democratic republic and adopt full proportional representation for elections.

"The protest rallies are meant to put pressure on the government to implement the decision of the parliament," said senior Maoist leader Ananta.

Thousands of Maoist supporters shouting anti-king slogans attended three separate rallies in the hill-ringed Kathmandu Valley, where the national capital is sited.

Ananta said similar demonstrations were organised in other parts of the mountainous nation.

Maoists say the government must move a formal motion in parliament's winter session starting on Monday to abolish the centuries-old Hindu monarchy.

The institution's popularity has plunged since 2005 when King Gyanendra grabbed absolute power, only to back down last year in the face of fierce protests.

The government says the Maoist demands are contrary to an earlier agreement to allow an elected assembly to decide the fate of the monarchy.

The row led the Maoists to quit the government in September and forced an indefinite postponement of elections planned for Nov. 22. Those polls, it was hoped, would cap a peace deal that ended a decade-long civil war in which 13,000 people died. (Reporting by Gopal Sharma, Editing by Mark Williams and Catherine Evans)

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