The European trio cited Iran's launch of a space vehicle and the unveiling of two new ballistic missiles in February as forming "part of trend of increased activity inconsistent" with the resolution, according to the letter sent to UN Secretary General Antonio Guterres.

UN Security Council Resolution 2231 -- adopted just after the 2015 nuclear deal -- calls on Iran "not to undertake any activity related to ballistic missiles designed to be capable of delivering nuclear weapons."

Tehran insists that its missile program is defensive and that it has no intention of developing a nuclear capability.

The three countries asked Guterres to "report fully and throughly on Iranian ballistic missile activity" in his next report, which is expected in June.

The letter from the European countries, which are signatories to the nuclear deal along with the United States and Russia, came nearly a month after the United States made a similar appeal to the council, saying it was time to bring back tougher international restrictions on Tehran.

President Donald Trump pulled the United States out of the nuclear accord in May last year and reimposed sanctions on Iran, citing concerns about missile development among its reasons.

At a council meeting in December, US Secretary of State Mike Pompeo called for tighter restrictions on Iran to curb its missile program but Russia flatly asserted that there was no proof that Iran's missiles can carry a nuclear payload.

The European countries said the Safir space launch vehicle used for a satellite blastoff on February 6 is based on two other missiles and uses technology closely related to the development of long-range and intercontinental ballistic missiles.

On February 7, the Iranian Islamic Revolutionary Guards unveiled the Dezful surface-to-surface missile which they claimed had a range of 1,000 kilometers, according to the letter sent on March 25.

During a public display in Tehran on February 4, Iran revealed a variant of the Khorramshahr ballistic missile that the letter said was "potentially an intermediate-range ballistic missile."

Iran reined in most of its nuclear program under the landmark nuclear deal with major powers but has kept up development of its ballistic missile technology.