(Adds chief of police's visit, details)

By Austin Ekeinde

PORT HARCOURT, Nigeria, Aug 11 (Reuters) - Gang fighting entered its sixth day in the anarchic oil city of Port Harcourt in southern Nigeria on Saturday with authorities acknowledging 11 deaths and residents and media putting the toll much higher.

Residents and security sources gave conflicting reasons for the gang war that erupted on Monday and has spread all over the sprawling industrial city, with street gunbattles breaking out several kilometres apart.

The fighting is typical of the way violence in Nigeria's oil heartland has degenerated from targeted attacks on the industry by militants pressing political demands to an uncontrollable wave of gang wars, abductions for ransom and armed robberies.

"We heard gunshots and dynamite blasts during the night and it went on for hours. When dawn broke we saw that the NNPC mega-station had been hit," said a resident of the Lagos Bus Stop area, referring to a state-run filling station.

The official News Agency of Nigeria (NAN) reported that fighters had also thrown dynamite at a radio station run by the government of Rivers state. NAN said troops had cordoned off the area and helicopters were circling above.

NAN quoted the Rivers state commissioner of police as saying the confirmed death toll from the week's fighting was 11 but it was possible police were not aware of some deaths.

Nigeria's chief of police, Mike Okiro, flew down to Port Harcourt to hold emergency meetings with the Rivers state governor and local army commander. He told reporters authorities planned to "clamp down" on the gangs.

Local radio stations, quoting witnesses and hospital staff, reported at least 10 deaths from Saturday's violence alone.

Residents said most of the victims were bystanders.

RESOURCE CONTROL

Violence escalated in early 2006 in the vast Niger Delta oil region when armed groups demanding control over oil revenues and an end to neglect by corrupt politicians started blowing up pipelines and oil wells and kidnapping foreign workers.

Their raids shut down at least a fifth of oil output from OPEC member Nigeria, the world's eighth-biggest exporter of crude, pushing up oil prices on world markets.

But over time, hostage taking became a commercial enterprise for copy-cat criminals while other forms of violence soared.

Politically motivated attacks have subsided since a new president took office on May 29 promising negotiations and efforts to develop the impoverished delta.

But the rebel Movement for the Emancipation of the Niger Delta, which was behind most of the attacks last year that shut down oil fields, has threatened to resume attacks.

The group's spokesman, who uses the pseudonym Jomo Gbomo, said it was considering new raids from the end of this month because it was disappointed with the government's approach to the demand for "resource control" or power over oil revenues.

"We will start with pipeline destruction and graduate to attacks on platforms and taking of hostages," he said in an email to Reuters on Saturday.

"They (the government) are prepared to build a few roads, schools, appoint some indigenes of the delta to insignificant roles, but make no mention of resource control," he added.

However, militant groups have been working on preconditions for talks with the government and some sources closely involved in the process have said they were optimistic that a more lasting truce could be achieved.

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