ABOARD A U.S. MILITARY AIRCRAFT - The top U.S. military officer said yesterday that he doesn't assume Iran's brief seizure of an Iraqi oil well is part of an orchestrated plan in Tehran to threaten its neighbors.

Adm. Mike Mullen also said he's worried about "the clock now running" on Obama administration efforts to keep the lines of communication open with Iran. The administration had given a rough deadline of the end of 2009 for Iran to respond to an offer of engagement and show that it would allay world concerns about its nuclear program.

Mullen, chairman of the Joint Chiefs of Staff, supports that offer and has said any military strike on Iran, whether by Israel or the U.S., should be a last resort.

The United States and others worry that Iran's program is intended to develop nuclear weapon. Iran says its work is designed to generate electricity but has defied international demands to prove it is not trying to build an atomic bomb.

The administration is beginning a push to get international support for more penalties against Iran as a result.

"I think signals are very clearly in the air that another set of sanctions, another resolution, that that's coming," he said.

"I grow increasingly concerned that the Iranians have been non-responsive. I've said for a long time we don't need another conflict in that part of the world," he said. "I'm not predicting that would happen, but I think they've got to get to a position where they are a constructive force and not a destabilizing force."

The administration is concerned about Iran's refusal to carry through on a tentative deal struck in October that called for Iran to ship most of its low-enriched uranium out of the country in exchange for fuel to run a research reactor.

The deal was seen by the United States and its negotiating partners as a step toward building confidence in Iran's claim that its nuclear program is to generate power, not weapons. The administration also stepped up sanctions talk after the revelation in September that Iran was secretly building a second uranium-enrichment facility near Qom.

Mullen, who spoke to reporters while flying from Germany back to the United States, said the oil well incident adds to his concerns about Iran's intentions toward neighboring Iraq and the rest of the world.

"I worry a great deal about . . . Iran and destabilizing as opposed to stabilizing," he said.

"And I worry about, you know, the clock now running on the dialogue and the engagement and sort of, where are we if that doesn't finish well? And certainly recent indications are . . .

they're not very responsive."

Meanwhile in Washington, senior Obama adviser David Axelrod said time was running out for Iran to cooperate. Sen. John McCain, R-Ariz., said the administration should act on its own to punish Iran and demonstrate support for Iranian dissidents.

Axelrod spoke on ABC's "This Week;" McCain appeared on "Fox News Sunday."