By Skye Wheeler

JUBA, Sudan, May 30 (Reuters) - South Sudanese officials complained on Friday that Khartoum was still keeping larger than normal numbers of soldiers in the disputed Abyei area after clashes between northern and southern troops earlier in May.

Tens of thousands of Sudanese civilians fled the oil-rich central town of Abyei during more than a week of clashes between northern and southern troops, prompting fears of further conflict.

"They're building up. There's no doubt about it," semi-autonomous south Sudan's Presidential Affairs Minister Luka Biong said, without giving details. He said north-south talks to re-establish peace in Abyei would continue on Saturday.

The southern army's deputy chief of staff, Salva Mathok, said there were nearly 11,000 northern soldiers in the Abyei area, where Khartoum had until recently kept only 3,000 to 4,000 troops.

Sudanese army officials could not immediately be reached for comment. Sudan had last week denied it was building up troops.

Northern and southern leaders have blamed each other for starting the fighting in Abyei in mid-May that left more than 20 northern soldiers and an unknown number of southerners dead.

Abyei, on Sudan's yet undecided north-south border, has been a point of contention since the former foes signed a peace deal in 2005 ending over two decades of civil war fought along ethnic, religious and ideological lines and complicated by oil.

Both the north and the south covet Abyei, which is close to oilfields that produce up to a half of Sudan's daily 500,000-barrel output.

Speaking to the southern parliament on Wednesday, Southern President Salva Kiir said he had agreed with Sudan's President Omar Hassan al-Bashir to withdraw southern troops together with a northern army brigade.

"(But) what we saw was more troops coming down the road to Abyei," he said, adding that the build-up of forces had been concentrated on the roads that link north and south Sudan, and are vital trade links for the landlocked south.

Mathok said that South Sudan's army was at least 29 km (18 miles) out of Abyei town. (Additional reporting by Mayen Benson; Editing by Giles Elgood)

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