* South Sudan reports heavy northern attacks in Abyei
* Oil-rich and fertile region disputed by north and south
(Adds new SPLA comments, mortar hits U.N. camp, details)
KHARTOUM, May 21 (Reuters) - South Sudan said northern forces had brought the main town of the disputed Abyei region under control after bombing several villages on Saturday, a day after tensions escalated in the border area.
The northern army could not be reached despite repeated attempts but the United Nations said it was deeply concerned about a troop build-up and reported fighting with heavy artillery in Abyei. It said a mortar had landed at a U.N. camp.
Southerners voted in January to become independent on July 9 but tensions escalated in the past days over the oil-producing region, the main dispute between both sides in the run-up to secession.
The violence comes a day before a delegation of the U.N. Security Council was due to hold talks with the government in Khartoum over Abyei.
The southern army (SPLA) said northern forces had bombed several villages in the afternoon and then entered the main town of Abyei with tanks.
"Abyei town is now under control of the SAF (Sudanese Armed Forces). They came with tanks," said SPLA spokesman Philip Aguer.
He said northern forces had bombed at least four villages, among them Todach and Tagalei, which it said had been already hit on Friday. [ID:nLAE985166]
The U.N. Mission in Sudan (UNMIS) said it could not verify the SPLA comments but said a mortar had landed inside a U.N. camp close to Abyei town. "There were no casualties," said spokesman Kouider Zerrouk.
Tensions escalated after the north accused the SPLA of attacking a convoy of Sudanese soldiers and U.N. peacekeepers in Dokura north of Abyei town late on Thursday.
The SPLA denied responsibility for the attack, which the United Nations said had taken place on a convoy of northern troops escorted by U.N. peacekeepers under a deal for both sides to withdraw forces from the disputed territory.
The North and South are supposed to have withdrawn all of their forces from Abyei by this week except for a special joint force made up of units from both sides.
The mainly Muslim North and the South, where most people are Christian or hold traditional beliefs, fought for decades in a civil war that killed an estimated 2 million people.
The war was ended by a 2005 peace deal that led to the referendum on southern independence, but the sides continue to clash over Abyei, which also contains fertile grazing land.
Earlier this month, at least 14 people were killed in clashes between northern and southern forces in Abyei. Both sides blamed each other for starting the violence.
Last month, Sudan's President Omar Hassan al-Bashir said he would not recognise the South's independence unless it gave up a claim on Abyei made in the south's draft constitution.
Abyei residents were also meant to have a referendum in January over whether to join the north or south. Disputes over who could vote derailed that ballot and talks over the status of the region have stalled.
North and south have also yet to agree how to share oil revenues and other assets prior to the secession. (Reporting by Ulf Laessing; Editing by Jon Hemming)
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