Boris Johnson says he is 'concerned' after Iran announced it had successfully tested a new medium-range missile.
Iranian state television broadcast footage on Friday showing the launch of a domestically-manufactured Khorramshahr ballistic missile.
No date or time were given for the test, which was the third such firing of a missile with a range of 2000km (1242 miles).
Foreign Secretary Boris Johnson said the test conflicted with a 2015 UN resolution with Iran over their nuclear program.
The test announcement came after Iranian President Hassan Rouhani pledged to increase the Islamic Republic's defensive power, including its missile capabilities and military forces, no matter whether its adversaries "like it or not".
Mr Rouhani made the remarks at a military parade in Tehran on Friday to mark the 37th anniversary of the outbreak of the start of the 1980-1988 war with Iraq.
In his address, the Iranian president first reviewed the Iran-Iraq War, saying that Iran's enemies should learn a lesson from the war and that Iran, as a nation playing an important role in safeguarding stability in the region, will continue to increase its defensive powers.
Iran also demonstrated its latest homegrown weaponry including tanks, radars, anti-ship missiles and air defense systems at the parade.
Earlier this week US President Donald Trump took aim at Iran, labelling it an "economically depleted rogue state" whose chief export is violence.
Mr Trump signalled a stronger approach to Tehran, questioning the 2015 deal with Iran struck by his predecessor Barack Obama.
He said world leaders "cannot abide" by the agreement if it "provides cover" for Iran to eventually build its nuclear programme.