(Updates with comment from Shell in paragraph 5)

By Austin Ekeinde

PORT HARCOURT, Nigeria, July 4 (Reuters) - Gunmen attacked an oil drilling rig and kidnapped five expatriates in the Niger Delta in southern Nigeria early on Wednesday, dealing a blow to a fledgling peace process in Africa's oil heartland.

This came as the rebel Movement for the Emancipation of the Niger Delta (MEND), responsible for most of the attacks that have crippled the Nigerian oil industry, called off a one-month truce. But the MEND spokesman said the group was not involved in the overnight raid on the Royal Dutch Shell <RDSa.L> rig.

"Early this morning there was an attack on a Shell facility at Soku. Armed men came in several boats, opened fire on security and abducted five expatriates," said an oil industry source in the regional capital Port Harcourt.

Industry sources said those kidnapped were two New Zealanders, one Australian, one Venezuelan and one Lebanese, and they gave a list of names. These details could not be immediately verified with the authorities.

Shell spokesman Precious Okolobo said no production was affected as the facility was an exploration rig operated by Lonestar, a Nigerian contractor to Shell.

Soku is an island in the coastal area of Rivers state where Shell has several oil rigs and a gas gathering plant. The area has been targeted by militants in the past.

The kidnappings raise to 15 the number of foreign hostages being held by different armed groups in the Niger Delta.

About 200 expatriates have been abducted since early 2006, prompting thousands of others to flee the Niger Delta. Most hostages were released unharmed in exchange for ransoms.

News of the attack and of the MEND's decision to call off its truce are a blow to President Umaru Yar'Adua, who came to power on May 29 promising urgent action to bring peace to the oil-producing region.

PEACE OVERTURES

Yar'Adua and his deputy, who originates from the delta, have made overtures to the rebels and tried to initiate a dialogue. Some have responded by releasing hostages, but others have said they were disappointed. Attacks and abductions have continued.

Nigeria is the world's eighth-biggest exporter of crude oil, but output is down by close to 700,000 barrels per day, or a quarter of total capacity. The outages are mostly due to attacks on oil facilities by the MEND over the past year and a half.

The MEND wants to hold direct talks with the Nigerian government on its demand for local communities in the impoverished delta to control oil revenues, the spokesman said.

"Whenever the Nigerian government is willing to dialogue directly with militia groups, we will be willing to make ourselves available," said the spokesman, who uses the pseudonym Jomo Gbomo, in an email to Reuters.

"We have called off our truce. It is ridiculous for our guns to remain silent while the military murders our civilians with impunity," he said.

The MEND had declared a truce until July 3 and had previously said that when that expired, it would assess efforts by the new government to resolve the crisis in the Niger Delta and decide whether to extend the truce or not.

"We may at some point if we have reason to," said Gbomo in response to a question on whether MEND would call a new truce.

"We seek to dialogue with the Nigerian government, through a neutral arbiter, on the issue of the return of the resources of the people of the Niger Delta, to their rightful owners." (Additional reporting by Estelle Shirbon in Abuja)

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