Iran vowed to continue with its missile and space program on Saturday, condemning new US sanctions as an attempt to undermine the international nuclear accord signed in 2015 between international powers and Tehran.

"We will continue with full power our missile program," Iranian Foreign Ministry spokesperson Bahram Ghasemi told state broadcaster IRIB on Saturday.

"We consider the action by the US as hostile, reprehensible and unacceptable, and it's ultimately an effort to weaken the nuclear deal," he added.

The US Treasury slapped new sanctions on Iran on Friday, a day after it test-fired a satellite-launch rocket into space. The sanctions targeted six subordinates of Shahid Hemmat Industrial Group, which develops Iran's ballistic missile program.

The US suspects Iran of trying to develop space technology for use in a long-range ballistic missile.

Flurry of US sanctions on Iran

The US Treasury sanctions in response to the space launch were the second in less than two weeks, and came as Congress sent a separate sanctions package targeting Russia, Iran and North Korea to US President Donald Trump's desk for a signature.

The Iran sanctions target the country for its ballistic missile program and the Islamic Revolutionary Guard Corps for "destabilizing" activities in the Middle East and human rights abuses.

In a joint statement Friday, Britain, France, Germany and the US - members of the so-called P5+1 group of countries, also including China and Russia, which negotiated the nuclear deal with Iran - condemned Iran's test space launch as "provocative" and "destabilizing."

"We call on Iran not to conduct any further ballistic missile launches and related activities," they said, calling the launch a violation of UN Security Council Resolution 2231, which endorsed the nuclear deal.

The US ambassador to the UN, Nikki Haley, expressed mistrust of Iran.

"Iran's widespread support for terrorists tells us we can't trust them. Iran's breaking its obligation on missile testing tells us we can't trust them. Yesterday's launch proves that yet again," she said.

Letter and spirit of nuclear deal

Under the Iran nuclear accord, Tehran agreed to drop its nuclear program in exchange for the lifting of crippling sanctions that had been imposed by international powers.

Iran argues the new sanctions, especially those passed by Congress, violate both the letter and spirit of the international nuclear agreement.

The wording of UN resolution authorizing the nuclear deal is vague on ballistic missiles. It "calls upon" Iran not to carry out work "designed to" deliver nuclear warheads.

However, Iran says its ballistic missiles are conventional weapons not "designed to" carry nuclear warheads even if they are "capable of" delivering them.

Since Iran is not pursuing nuclear weapons and has given up its program, Tehran argues, the UN resolution does not apply to its ballistic missiles. Iran says its missile programs are for defensive purposes. 

Iranian Foreign Minister Javad Zarif on Friday tweeted his country's position on the nuclear deal (JCPOA).

Ghasemi, Iran's Foreign Ministry spokesman, said the country's military and missile development were domestic issues that no country had a right to intervene in.

"Iran does not recognize any limits to its scientific and technological progress and will not wait for the approval or permission of any country regarding the activities of its scientists and experts," the spokesman said.

Both the US State Department and the International Atomic Energy Agency have confirmed that Iran is abiding by the nuclear agreement and has dismantled its nuclear weapons program.

Deliberately undermining deal?

The Trump administration is reviewing the nuclear accord and has upped its hostile rhetoric against Iran, suggesting the US could "tear up" the deal as it reverts to a policy of regime change in Tehran. Trump entered the White House vowing to be the best friend of Israel, whose right-wing government is against the nuclear deal and is concerned over Iran's influence in the region. 

But some within the Trump administration and Congress are urging Trump to hold off for now, concerned that a unilateral US exit from the accord would isolate Washington from its European allies.

"You can only tear up the agreement one time," said Bob Corker, the chairman of the Senate Foreign Relations Committee, this week at an event organized by The Washington Post newspaper.

Since Iran is not now developing a nuclear weapon, he said, "you want the breakup of this deal to be about Iran; you don't want it to be about the United States, because we want our allies with us."

The US is adding demands to the nuclear deal and wants to renegotiate it, he said, including requesting access to Iranian military facilities that would certainly be rejected by Tehran.

"If they don't let us in," Corker said, then "boom."

Broader regional struggle 

The ratcheted-up tensions between the two adversaries come as Iran uses asymmetrical power and proxies to extend its influence across the Middle East, especially in Iraq and Syria.

US ally Israel has been particularly concerned about Iran and Hezbollah's expansion in Syria as Tehran helps the Assad regime battle rebels and jihadists.

Meanwhile, tensions between Iran and Gulf Arab states have been flaring up, raising the specter of hot conflict that has so far been political or played out through proxies. 

Iran and its rival Saudi Arabia, a US ally, are the main actors challenging each other for influence across the region, from Yemen and Syria to the Persian Gulf. 

Iran views a missile capability as necessary to defend itself and counterbalance Saudi Arabia, which has been on a weapons-buying binge in the past several years that has given it technological military superiority.