Anchorage: A subsidiary of Royal Dutch Shell received federal approval on Friday for drilling exploratory wells in the Chukchi Sea off Alaska's northwest coast but with conditions that raised concerns with the state's congressional delegation.

Approval by the federal Bureau of Ocean Energy Management (BOEM) came with the catch that Shell must lop 38 days off the short summer open-water drilling season to make sure it has time to cope with a spill or a wellhead blowout before sea ice moves in.

"While today's news that BOEM has issued conditional approval for Shell's Chukchi leases might seem welcoming at first glance, the devil is in the details," Alaska's lone US representative, Don Young, said in a statement.

Both Alaskans and pet-roleum companies that have invested billions are looking for certainty and progress, he said.

"Unfortunately this ‘conditional' approval won't bring much of either," Young said.

Shell Alaska spokesman Curtis Smith said the company is evaluating conditions outlined in the approval, including the stipulation that potentially limits the drilling season.

"We are concerned this unwarranted restriction could severely impact our ability to deliver a complete Chukchi programme," Smith said in written comments.

Threat to villagers'

A spokesman for one of the environmental groups, Oceana, said the approval was made despite gaps in basic scientific knowledge of the region.

"We don't have any demonstrated capacity to respond to a spill in Arctic conditions," said Mike LeVine in Juneau.

Rosemary Ahtuantaruak, originally from the Alaska North Slope Village of Nuiqsut and now a tribal liaison official with the Alaska Wilderness League, said drilling is a threat to coastal villagers' health.

"They didn't learn from the Exxon Valdez," she said. "They didn't learn from the Gulf of Mexico."

The Chukchi is part of vast Arctic Ocean outer continental shelf reserves that the federal government estimates at 26.6 billion barrels of recoverable oil and 3.68 trillion cubic metres of natural gas.

The state of Alaska, with an eye toward dim-inishing volumes of crude moving through the trans-Alaska pipeline, has pushed strongly for companies to develop offshore reserves.

Strong opposition

Shelf Gulf of Mexico Inc proposes a multi-year exploration drilling programme in the Chukchi beginning in July. The plan proposes drilling up to six wells in the Burger Prospect about 112 kilometres off the coast in water about 43 metres deep. Shell contends it can conduct safe operations in the relatively shallow water.

Exploratory drilling is strongly opposed by environmental groups and some Alaska Native groups that want to keep large-scale industrial development out of the Arctic Ocean because of risks to whales, polar bears, walrus and other marine species, and to protect the subsistence lifestyle of Native Alaskans who depend on the ocean for subsistence hunting and harvesting.