Clinton put herself at odds with Obama's administration late on Tuesday by describing the Arctic as a "unique treasure" and "not worth the risk of drilling" because of multiple environmental risks.

Obama's administration on Monday gave Royal Dutch Shell final approval to resume drilling into an oil-bearing rock, 2,400 meters (8,000 feet) below the ocean floor off northern Alaska.

Shell's original leases were obtained from the administration of the previous Republican president, George W. Bush.

White House spokesman Frank Benenati deflected environmentalists' condemnation, saying Obama's team had initiated heavy investment in renewable energy sources ahead of December's UN climate summit in Paris.

It had also "taken steps to ensure safe and responsible development" of US energy sources, he said, referring to the 2010 Deepwater Horizon oil spill in the Gulf of Mexico.

Pitching to environmentalists

Tuesday's remark by Clinton in a Twitter post marked a break with Obama as part of her recent overtures to Democratic environmentalists, whose support she will need to secure her party's official nomination.

Her liberal challenger, US Senator Bernie Sanders of Vermont, was among a group of senators who sent the Obama administration a letter opposing Arctic drilling in May.

Environmentalists say any spill would severely endanger maritime fauna, such as whales and plankton, in a region already vulnerable to climate change. They also argue that added fossil fuel usage will only exacerbate climate warming.

Shell says Arctic oil is need to meet growing global demand.

Rebecca Noblin, Alaska director for the Center for Biological Diversity, described the White House stance as "perplexing," given Obama's recent statements that he wants to fix climate change.

"It's like a doctor diagnosing a patient but then refusing to write a prescription," Noblin told the Associated Press.

Obama's Republican rivals in Congress, as well as industry officials, have often accused the administration of hindering oil and gas extraction on federal lands.

Trump leads Republican field

Meanwhile, rhetorically brash still leads the 17-candidate Republican field for next year's US presidential race.

A new national CNN/ORC survey put Trump at 24 percent, clearly ahead of second-placed former Florida Governor Jeb Bush at 13 percent. Retired neurosurgeon Ben Carson came in third.

Those surveyed were dubious, however, on Republican chances of winning the White House. Asked if chances were better if Trump ran, only 38 percent agreed. Another 58 percent said Republican chances would be better without him.

The first primaries to narrow the Republican field are more than five months away. Election day is still nearly 15 months away.

ipj/cmk (AFP, Reuters, AP)