Tensions High, US Warns Iran Not to Block Shipping 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. No shots were fired and the speedboats backed off. FILE - In this Jan. 5, 2012 file photo, Defense Secretary Leon Panetta speaks at the Pentagon. Tensions flaring, the Obama administration warns Iran through public and private channels against any action that threatens the flow of oil from the Persian Gulf. Some experts fear the risk of open conflict with Tehran appears higher than at any point since President Barack Obama took office, perhaps from U.S. moves to enforce open shipping through the Strait of Hormuz or even a military strike from Israel. (AP Photo/Pablo Martinez Monsivais, File) Close For several reasons, 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. The U.S. still hopes that international pressure will persuade Iran to back down on its disputed nuclear program, but the Islamic regime shows no sign it would willingly give up a project has become a point of national pride. A nuclear bomb, or the ability to quickly make one, could also be worth much more to Iran as a bargaining chip down the road. Time is short, with Iran making several leaps toward the ability to manufacture a nuclear weapon if it chooses to do so. Iran claims its nuclear development is intended for the peaceful production of energy. Meanwhile, several longstanding assumptions about U.S. influence and the value of a targeted strike to stymie Iran's progress toward a nuclear weapon have changed. For one, the White House is no longer confident it could prevail on Israel not to launch such a strike. An escalating covert campaign of sabotage and targeted assassinations highlighted by this week's killing of an Iranian nuclear scientist may not be enough to head off a larger shooting war and could prod Iran to strike first. The brazen killing of a young scientist by motorcycle-riding bombers is seen as almost surely the work of Israel, according to U.S. and other officials speaking on condition of anonymity to discuss intelligence matters. The killing on a Tehran street followed the deaths of several other Iranians involved in the nuclear program, a mysterious explosion at an Iranian nuclear site that may have been sabotage and the apparent targeting of the program with an efficient computer virus.