Environmental organizations urged the Obama administration not to allow oil giant Shell to begin planned exploratory drilling in arctic seas off Alaska this summer.

After a series of delays, Shell was to begin its long-planned drilling in the Beaufort and Chukchi seas during the brief ice-free period this summer. But the company's window for drilling is narrowing, as it faces a Sept. 24 deadline when it must cease operations in hydrocarbon-bearing zones in the Chukchi and by Oct. 31 in the Beaufort.

The group's appeal -- in a letter Thursday addressed to U.S. Interior Secretary Ken Salazar -- to deny essential permits Shell needs to begin working on wells this summer came ahead of the secretary's planned weekend visit to Alaska.

Salazar told Politico that "we're not going to Alaska to do any kind of announcement on the Arctic and Shell," and a spokesman said the secretary's agenda includes "balanced energy development, management of public lands and issues facing Alaska's native and rural communities."

The visit to Alaska is Salazar's fourth since assuming office in January 2009.

Salazar has said that he anticipates a final decision on Shell's plans by mid-August, The New York Times reports.

While company officials this week said Shell was completing preparations for the Arctic Ocean drilling, the project has faced weeks of delays related to mechanical problems and persistent sea ice, the Times report states.

"Your department, together with President Obama, has consistently assured the American public that Shell's frontier drilling program in the Arctic Ocean would be the safest and most scrutinized in the history of our nation," the environmentalists' letter says.

The groups include the Alaska Wilderness League, the Center for Biological Diversity, Defenders of Wildlife, Greenpeace and the National Audubon Society.

"The bottom line is that Shell is not living up to its promises and is trying to drill this summer even while serious problems remain, including the persistence of hazardous icy conditions in the Arctic," it states.

"In light of the significant missing scientific information, lack of preparedness and Shell's broken promises, we urge you to deny Shell its [drilling permits] for Arctic drilling this season," the letter continues.

Last week, U.S. Sen. Lisa Murkowski, R-Alaska, said that the Interior Department should consider extending Shell's Arctic drilling window beyond September and October.

"I think they should be open to extending it, and I believe they will if it is determined that the ice conditions are such that there will be an adequate period of time ... for Shell to get out of the water," Murkowski, the top Republican on the Energy and Natural Resources Committee, said of the deadline, The Hill reports.