The US government was looking into reports about Iran's ballistic missile testing last month, the White House said on Wednesday.
"The Iran ballistic missile programme has been... a source of concern for years," White House spokesman Josh Earnest told reporters during a daily news briefing.
The US was deepening its cooperation with partners to counter Iran's programme, he said.
Iran tested a new medium-range ballistic missile last month, US media reported on Monday, citing a senior US official.
Western intelligence said the test was held on November 21 near Chabahar, a port city in Iran's Balochistan province near the border with Pakistan, Fox News reported.
It quoted the US official, who spoke on condition of anonymity, as saying that the new test was in breach of two United Nations Security Council resolutions.