FAIRFAX, Va. - Mitt Romney broadened his criticism of President Obama's handling of attacks in the Middle East on Thursday, saying the killing of four Americans in Libya demonstrated the need to strengthen America economically and militarily.

"As we watch the world today, sometimes it seems that we are at the mercy of events instead of shaping events," he said at a campaign rally in the battleground state of Virginia. "A strong America is essential to shape events."

The Republican presidential candidate came under withering, bipartisan criticism Wednesday for his response to attacks on U.S. diplomatic offices in Egypt and Libya that led to the death of an ambassador and three other Americans.

At his event Thursday, Romney mentioned the crisis only briefly, focusing his remarks on the need for more assertive American leadership and charging Obama with undercutting the strength of the U.S. military.

Obama, wrapping up a two-day campaign swing, reiterated his vow to avenge the deaths of the Americans.

"We are going to bring those who killed our fellow Americans to justice," he said at a rally in Colorado, another swing state. "I want people around the world to hear me: To all those who would do us harm, no act of terror will go unpunished."

Though neither candidate mentioned his opponent by name Thursday in discussing the turbulence in the Middle East, the violence abroad replaced the economy in the campaign's spotlight.

Public opinion polls have shown voters giving Obama higher marks on dealing with foreign policy than Romney.

Romney was on the defensive Wednesday for accusing the Obama administration of apologizing to Egyptian protesters. He referred to a statement issued by the U.S. Embassy in Cairo intended to calm the situation that was released hours before the attacks occurred there and in Libya.

Romney in an interview Thursday stood by his criticism of the embassy statement, which condemned "the actions by those who abuse the universal right of free speech to hurt the religious beliefs of others."

"I think the statement was an inappropriate statement," he said, according to excerpts of an interview with ABC News's George Stephanopoulos released Thursday evening by the network. "I think it was not directly applicable and appropriate for the setting."

Campaign aides say Romney's remarks are consistent with his view on foreign policy and the positions he described in his 2010 book, No Apology. Romney, they say, thinks that Obama and his team have focused on trying to forge relationships with countries that pose a threat, such as Iran, at the expense of long-standing allies, including Israel.

Democrats counter that Romney is reckless and lacks the foreign-policy experience needed for the presidency. Reacting to Romney's comments on the Cairo embassy's statement, Obama, in an interview with CBS News on Wednesday, said his opponent has "a tendency to shoot first and aim later."