* Clashes spark fears ahead of independence
* South's ruling party says rebels "better take" offer
By Jeremy Clarke
JUBA, Sudan, April 5 (Reuters) - South Sudan's government renewed an amnesty offer to rebel militia groups on Tuesday to try to calm tensions in the region before its expected independence in July.
Clashes between the southern army (SPLA) and forces loyal to renegade military leaders have killed hundreds this year and sparked concern the oil-producing region will struggle to impose law and order after secession on its vast territory.
Before January's independence referendum -- when the south voted to secede from the north -- southern President Salva Kiir offered amnesty to southern militia groups, and violence fell as southerners awaited their historic vote.
But fighting between militiamen, who accuse the government of not representing the people, and the army has flared since.
Senior southern official Pagan Amum said on Tuesday all militia were welcome to the amnesty should they want it, despite attacks the SPLA have called a "massacre of civilians".
"Our message to all these militia groups is that it is time for them to heed to the call of reconciliation," Amum told reporters at Juba's airport.
"Even if they were working against their own people ... They are all welcome to put down their guns, there is amnesty that has been offered to them and they had better take it."
Amum once again accused the southern militia of being backed and armed by the northern government -- a charge that Khartoum and the rebel groups deny.
Militia groups in turn accuse the southern army of attacking them as they waited for the amnesty offer at their bases, the rebels and a diplomatic source have said.
Think tank International Crisis Group (ICG) has said the violence is a return to pre-referendum patterns of fighting that threatens to deepen instability in the south.
Some analysts say the south, which has long suffered from tribal and ethnic divisions, risks becoming a failed state that could destabilise east Africa if it fails to maintain security.
"The post-election rebellions are ... not unfamiliar in a still militarised region where disgruntled actors resort to arms to extort influence or achieve ends they believe cannot be achieved through other channels," ICG said in a report.
"The recent fighting, including a sometimes heavy-handed SPLA response, risks continued instability, poses serious danger to civilians (many have already been killed in the crossfire) and threatens further polarisation between ethnic groups and their political leaders."
The independence referendum was the result of a peace agreement in 2005 which ended decades of north-south civil war. Fought over differences in ethnicity, religion, ideology and oil, the war killed at least two million people. (Editing by Deepa Babington)
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