Tehran, Iran ? Iran stepped up its warnings to the United States on Thursday, with the nation’s supreme leader saying Tehran will strike U.S. interests around the world if his country is attacked.

Ayatollah Ali Khamenei’s words were also likely meant as a show of toughness to rally Iranians, who are increasingly worried about the possibility of American military action as the two countries’ standoff has grown more tense.

Days earlier, an Iranian diplomat was detained in Iraq in an incident that Iran blamed on America. The United States denied any role. The U.S. also says it has no plans to strike Iran militarily, but has sent a second aircraft carrier to the Persian Gulf to show strength in the face of rising Iranian regional influence.

But many in Iran say they fear attack. Iranian media and Web sites have almost daily commentaries on a possible U.S. attack – some of them blaming hard-line President Mahmoud Ahmadinejad for the deterioration in the already sour U.S.-Iranian relations by his provocative rhetoric against America and Israel.

Speaking to Iranian air force commanders, Khamenei said, “The enemy knows well that any invasion would be followed by a comprehensive reaction to the invaders and their interests all over the world.” His words were carried on state-run TV.

In Washington, State Department spokesman Tom Casey, asked about the comments, said American efforts on Iran focus on diplomacy. The two are in dispute about Iran’s nuclear program and its role in Iraq.

Even as Iran’s rhetoric has escalated, it increasingly has insisted it is open to a diplomatic solution to its standoff with the West. Iran’s top nuclear negotiator, Ali Larijani, said Wednesday he would meet European officials for talks on Iran’s nuclear program during a security conference this weekend in Munich, Germany.

Tehran’s ambassador to the United Nations, Javad Zarif, wrote in a column published Thursday in The New York Times that the United States was trying to make Iran a “scapegoat” for Washington’s failures in the Mideast, particularly Iraq. He warned that efforts to isolate Iran would backfire on the United States, increasing sectarian tensions in the region.

The United States is reaping “the expected bitter fruits of its ill-conceived adventurism” in Iraq, he said.

Zarif also made clear, however, that Iran wants to be part of some regional and international solution to calm Iraq, despite U.S. rejection of the idea of reaching out to Iran for help.