State media said the tests included the first night launch of the Shahab-3 missile, said to have a range of 2,000km (1,240 miles), along with shore-to-sea, surface-to-surface and sea-to-air missiles.
Secretary of State Condoleezza Rice said the US had increased its security in the region and Iran should not be "confused" about US capabilities.
Israel has responded to the missile tests by putting on display one of its aircraft that it says can spy on Iran.
The state-run Israel Aerospace Industries says it has equipped its Eitam aeroplane, unveiled a year ago, with sophisticated intelligence-gathering systems.
Mr Barak spoke of the "potential for accords, particularly with the Palestinians and the Syrians", but stressed that the situation was very complex.
Quoted by Israeli news website Ynet, Mr Barak said: "We must work towards an accord - but if not, then we must strike our enemy when it is required."
He also warned that Israel must consider the reactions from other nations in the region that could be provoked by action against Iran.
"The responses of our adversaries must be taken into account. Hamas and Hezbollah and the Syrians and the Iranians - there is activity all around us. And there exists a potential for confrontation."
Iran has been accused of doctoring an image from its missile tests
Meanwhile, the AFP news agency has issued a warning that a still image of the missiles being launched, one of several distributed by Iran, was "apparently digitally altered".
The photograph, published on the Iranian Revolutionary Guards website and reproduced by media organisations - including the BBC News website - showed four missiles taking off from a desert launch-pad.
But a similar image, issued by the Associated Press, shows one of the missiles still in its launcher after apparently failing to fire.
The BBC News website's picture editor, Phil Coomes, said: "Having examined the photograph from AFP, it can be seen that parts have been edited, with smoke trails and parts of the foreground being cloned."
In recent weeks, both Israel and Iran have been testing and showing off their military hardware, each saying that in the event of provocation it is more than capable of defending itself.
The Israeli air force recently carried out a large-scale exercise over the Mediterranean - regarded by many observers as a dress rehearsal should the order be given to attack Iran's nuclear facilities. Israel believes Iran is building nuclear weapons, although Tehran insists its nuclear programme is purely for civilian energy.
Western leaders have been trying to convince Iran to stop enriching uranium, which it has continued doing despite sanctions from the UN and the European Union.
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Iran test-fires missiles in the Gulf - footage from Iranian state TV
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FROM OTHER NEWS SITES
MSNBCIran test-fired more long-range missiles overnight in a second round of exercises meant to show that the country can defend itself against any attack by the United States or Israel, state television reported Thursday. - 14 hrs ago
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Daily MailIran ignores threats and fires a second volley of test missiles - 14 hrs ago
HaaretzIsrael to showcase plane it says is capable of spying on Iran - 15 hrs ago
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