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Associated Press
In this Jan. 12, 2012 file photo, White House Press Secretary Jay Carney speaks during the daily briefing at the White House in Washington.

WASHINGTON — Tensions rising by the day, the Obama administration said Friday it is warning Iran through public and private channels against any action that threatens the flow of oil from the Persian Gulf. The Navy revealed that two U.S. ships in and near the Gulf were harassed by Iranian speedboats last week.

Spokesmen were vague on what the United States would do about Iran's threat to block the strategic Strait of Hormuz, but military officials have been clear that the U.S. is readying for a possible naval clash.

That prospect is the latest flashpoint with Iran, and one of the most serious. Although it currently overshadows the threat of war over Iran's disputed nuclear program, perhaps beginning with an Israeli military strike on Iran's nuclear structure, both simmering crises raise the possibility of a shooting war this year.

"We have to make sure we are ready for any situation and have all options on the table," Defense Secretary Leon Panetta said, addressing a soldier's question Thursday about the overall risk of war with Iran.

Navy officials said that in separate incidents Jan. 6, three Iranian speedboats — each armed with a mounted gun — briefly chased after a U.S. Navy ship just outside the Gulf near the Strait of Hormuz and a U.S. Coast Guard cutter in the northern Gulf.

The risk of open conflict with Tehran appears higher in this election year than at any point since President Barack Obama took office with a pledge to try to bridge 30 years of enmity. A clash would represent a failure of U.S. policy on several fronts and vault now-dormant national security concerns into the presidential election contest.