AFP/ Yangon

Myanmar on Thursday signed a ceasefire with eight ethnic minority armies in a step towards ending decades of civil war, a move weakened by the refusal of several other rebel groups to join the deal.

The truce is the fruit of more than two years of negotiations and was a key goal of reformist President Thein Sein ahead of November elections, which are likely to sweep his army-backed party from power.

In a lavish televised signing ceremony in the remote capital Naypyidaw, Thein Sein said the deal would give "an inheritance of peace" to future generations.

State-backed newspaper Global New Light of Myanmar said the agreement may herald a "fully fledged peace process that will end more than 60 years of civil conflict".

But hopes for a full nationwide ceasefire before the November 8 election crumbled recently after several rebel groups baulked at any deal without the inclusion of all insurgent forces -- notably smaller organisations locked in conflict with the army.

Myanmar's powerful army chief and rebel representatives in ethnic dress attended the signing, while representatives from China, India, the European Union and United Nations were among the witnesses.

In a statement, the US State Department welcomed "a critical first step" in building sustainable peace, but raised concerns over continuing fighting in northern Kachin and Shan state.

The deal enables the groups involved to begin political dialogue with the government -- a longstanding demand of ethnic minorities calling for greater autonomy.

But much depends on the actions of Myanmar's army, which is not under civilian control.

Myanmar's military held the country in an iron grip for decades and retains significant political clout, including holding a quarter of parliament's seats.

"The real test now lies ahead, in demonstrating that this partial agreement can bring tangible political and security benefits," said independent analyst Richard Horsey, who attended the ceremony.

- Election jitters -

The ceremony comes during a week of political jitters in Myanmar.

On Tuesday election officials briefly suggested delaying the November polls -- the first credible general elections in decades in the formerly military-run nation.

Authorities had cited widespread flooding for a proposed postponement, but after angry rejection by Aung San Suu Kyi's opposition party they dropped the idea.

The veteran democracy activist-turned-politician is expected to lead her party to huge gains at the polls, even though she is currently barred from being president by the junta-drafted constitution.

She did not attend the ceasefire ceremony in person, but insists any government led by her National League for Democracy is committed to peace.

Myanmar has been torn by civil wars since the end of British colonial rule in 1948.

The army used the conflicts to justify its grip on power and has been accused of widespread abuses across ethnic areas.

The government has sought to reward groups signing the deal by removing them from lists of unlawful organisations, meaning their members can now travel freely and take part in politics.

These include the Karen Nation Union, whose armed wing battled government forces in Myanmar's east from 1949 in one of the world's longest civil wars.

But with fighting still raging in parts of the country, election officials this week said polls can not be carried out in areas battered by conflict or outside government control.

Major rebel groups in the north, including the Kachin Independence Army, have refused to sign the ceasefire.

In Kachin more than 100,000 people have been displaced since a ceasefire between rebels and the state army collapsed in 2011.