Iran test-fires missiles in the Gulf - footage from Iranian state TV
The US has said it will not hesitate to defend its interests and those of its allies as Iran continues missile tests.
Secretary of State Condoleezza Rice said the US had increased its security in the region and Iran should not be "confused" about US capabilities.
Iran tested missiles on Wednesday that could reach Israel, and on Thursday carried out further tests.
Meanwhile French energy giant Total has said it will not invest in Iran because it is too politically risky.
New tests
Condoleezza Rice was speaking during a visit to Georgia.
She said: "We take very strongly our obligation to defend our allies and we intend to do that.
Map of missile range
Tensions mount over Iran
Easy gas riches on hold for Iran
"In the Gulf area, the United States has enhanced its security capacity, its security presence and we are working closely with all our allies... to make [sure] they are capable of defending themselves."
The Iranian military said on Thursday its Revolutionary Guards had carried out further medium- and long-range missile tests overnight.
The tests included the first night test 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, state media reported.
The BBC's Jon Leyne in Tehran says this appears another gesture of defiance following the international condemnation of Wednesday's tests. Media reports appeared to be delivered as a matter of pride. Ms Rice said it was about time Iran "got on the right side of the international community".
The first test of the updated Shahab-3 missile, which could strike Israel, was on Wednesday.
Gen Hoseyn Salami, the Guards' air force commander, said the tests demonstrated Iran's "resolve and might against enemies who in recent weeks have threatened Iran with harsh language".
State media quoted him as saying: "Our hands are always on the trigger and our missiles are ready for launch."
William Burns, the top official handling Iranian issues at the US state department, said the launch was "very disturbing, provocative and reckless".
On Thursday, Israel responded to the missile tests by saying it would exhibit publicly an advanced aircraft that could spy on Iran.
'Big blow'
Meanwhile, the head of Total, Christophe de Margerie, told the Financial Times the company's planned development of the huge South Pars gas field in southern Iran would not go ahead.
"Today we would be taking too much political risk to invest in Iran because people will say: 'Total will do anything for money'," he said.
Total was the last major Western energy group to have seriously considered investing in the country's huge gas reserves.
Analysts say the move will be a big blow to the Iranian energy industry.
It means Iran is now unlikely to significantly increase its gas exports until late into the next decade, they add.
US warns Iran on missile threat
Iran test-fires missiles in the Gulf - footage from Iranian state TV
The US has said it will not hesitate to defend its interests and those of its allies as Iran continues missile tests.
Secretary of State Condoleezza Rice said the US had increased its security in the region and Iran should not be "confused" about US capabilities.
Iran tested missiles on Wednesday that could reach Israel, and on Thursday carried out further tests.
Meanwhile French energy giant Total has said it will not invest in Iran because it is too politically risky.
New tests
Condoleezza Rice was speaking during a visit to Georgia.
She said: "We take very strongly our obligation to defend our allies and we intend to do that.
Map of missile range
Tensions mount over Iran
Easy gas riches on hold for Iran
"In the Gulf area, the United States has enhanced its security capacity, its security presence and we are working closely with all our allies... to make [sure] they are capable of defending themselves."
The Iranian military said on Thursday its Revolutionary Guards had carried out further medium- and long-range missile tests overnight.
The tests included the first night test 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, state media reported.
The BBC's Jon Leyne in Tehran says this appears another gesture of defiance following the international condemnation of Wednesday's tests. Media reports appeared to be delivered as a matter of pride. Ms Rice said it was about time Iran "got on the right side of the international community".
The first test of the updated Shahab-3 missile, which could strike Israel, was on Wednesday.
Gen Hoseyn Salami, the Guards' air force commander, said the tests demonstrated Iran's "resolve and might against enemies who in recent weeks have threatened Iran with harsh language".
State media quoted him as saying: "Our hands are always on the trigger and our missiles are ready for launch."
William Burns, the top official handling Iranian issues at the US state department, said the launch was "very disturbing, provocative and reckless".
On Thursday, Israel responded to the missile tests by saying it would exhibit publicly an advanced aircraft that could spy on Iran.
'Big blow'
Meanwhile, the head of Total, Christophe de Margerie, told the Financial Times the company's planned development of the huge South Pars gas field in southern Iran would not go ahead.
"Today we would be taking too much political risk to invest in Iran because people will say: 'Total will do anything for money'," he said.
Total was the last major Western energy group to have seriously considered investing in the country's huge gas reserves.
Analysts say the move will be a big blow to the Iranian energy industry.
It means Iran is now unlikely to significantly increase its gas exports until late into the next decade, they add.
