When asked during an exclusive interview on "Good Morning America" what the United States should do, Sen. Barack Obama, the Democratic candidate, replied, "What we should have been doing from the start, instead of engaging in over-the-top rhetoric, what we should be doing is gathering our allies together in a serious effort to apply sanctions to Iran and encourage them to change their behavior."
Asked by Diane Sawyer whether he believed Israel had a right to a preemptive strike against Iran, Obama said, "Israel always has the right to protect itself from serious threats and Iran is a serious threat."
Republican presidential candidate Sen. John McCain declined in an exclusive interview with ABC News' Charlie Gibson to endorse an Israeli air strike on Iran's nuclear facilities.
"I can't know whether a strike would be justified because I don't know the progress or the nature or the significance of the threat," McCain said.
"We cannot allow a second holocaust as I said, but I do believe that there's many options," McCain added.
The Republican agreed with Obama that the U.S. must rally other countries to impose tough sanctions on Iran, but he singled out Russia for its reluctance to crack down on Iran.
McCain took a swipe at Obama's willingness to negotiate with Iran.
"I've stated on a number of occasions that to sit down without preconditions is a serious mistake because I think it lends prestige and status to anyone who is dedicated to the extinction of its neighbor," McCain said.
In a statement issued by his campaign, McCain said the Iran missile tests "demonstrate the need for effective missile defense now and in the future."
U.S. Secretary of State Condoleezza Rice echoed McCain, calling today's tests "evidence that the missile threat is not an imaginary one."
"Those who say that there is no Iranian missile threat against which we should build a missile defense system perhaps ought to talk to the Iranians about their claims," Rice said while traveling to Sofia, Bulgaria.
U.S. plans for a missile shield and an agreement signed Tuesday with the Czech Republic to allow a tracking system on its soil prompted Russia to say ominously it would use "military-technical methods" if it is built.
ABC NEWS's Kirit Radia and the Associated Press contributed to this report.