WASHINGTON — The deadly attack on Americans in Libya fueled a harsh escalation of the presidential campaign in the United States on Wednesday as Mitt Romney assailed President Obama’s handling of the situation, while Democrats accused Mr. Romney, the Republican nominee, of politicizing an international crisis.


A back-and-forth between the Romney and Obama campaigns over attacks in Libya and Egypt represented a rare partisan exchange over a foreign policy crisis and underscored the intensity and stakes of the campaign with less than two months until Election Day. The crisis has also rapidly emerged as a test of Mr. Romney’s handling of a fast-breaking international situation.


The news of the deaths of J. Christopher Stevens, the ambassador to Libya, and three other Americans emerged on Wednesday after violence spilled over the American Consulate in Benghazi and demonstrators stormed the American Embassy in Cairo.


After expressing sorrow about the deaths, Mr. Romney told reporters on the campaign trail that the Obama administration had tried to appease Islamic extremists who should have been condemned instead. He said a statement issued by the American Embassy in Cairo before the deaths criticizing an anti-Islamic video was “akin to an apology” and a “severe miscalculation.”


“The first response of the United States must be outrage at the breach of the sovereignty of our nation, and apology for American values is never the right course,” Mr. Romney said, speaking at a campaign stop in Jacksonville, Fla. He added, “They clearly sent mixed messages to the world.”


The comments echoed a statement that the Republican nominee released on Tuesday. Mr. Romney had pledged not to criticize Mr. Obama on the anniversary of the Sept. 11 attacks, but by Tuesday evening, his campaign reversed course, releasing early a statement that had been embargoed until midnight that criticized the president’s handling of violence at the American posts.


“I’m outraged by the attacks on American diplomatic missions in Libya and Egypt and by the death of an American consulate worker in Benghazi,” Mr. Romney said in a statement that went out just before 10:30 p.m. “It’s disgraceful that the Obama administration’s first response was not to condemn attacks on our diplomatic missions, but to sympathize with those who waged the attacks.”


He was referring to the embassy statement condemning an American-made Web film denouncing Islam that was the catalyst for the violence. However, the embassy’s statement was released in an effort to head off the violence, not after the attacks, as Mr. Romney’s statement implied. (Though the embassy staff in Cairo later said on Twitter that its original statement “still stands” — a message it then tried to delete — the Obama administration disavowed the embassy’s statement.)


Mr. Romney’s statement, which also came out before news that Mr. Stevens had been killed in the attacks, quickly came under fire from Democrats, who accused him of politicizing the violence in the Middle East at a particularly delicate time.


“We are shocked that, at a time when the United States of America is confronting the tragic death of one of our diplomatic officers in Libya, Governor Romney would choose to launch a political attack,” Ben LaBolt, a spokesman for the Obama campaign, said in an e-mail statement.


In his official statement issued from the White House Rose Garden on Wednesday, Mr. Obama condemned “this outrageous and shocking attack” and did not directly respond to Mr. Romney’s criticism or take questions from reporters.


“Make no mistake, we will work with the Libyan government to bring to justice the killers who attacked our people,” he said as Secretary of State Hillary Rodham Clinton stood by his side.


But Mr. Obama implicitly rebutted the notion that his administration had apologized for American values.


“We reject all efforts to denigrate the religious beliefs of others,” he said. “But there is absolutely no justification to this kind of senseless violence. None. The world must stand together to unequivocally reject these brutal attacks.”