The United States has extended sanctions against Iran by targeting the construction sector, which Washington has linked to Iran's Revolutionary Guards, and has offered exemptions from sanctions to foreign companies engaged in peaceful nuclear activities in Iran.

A statement by US Secretary of State Mike Pompeo said the Iranian construction sector is under direct or indirect control of Iran's Revolutionary Guards, which the United States has labeled a foreign terrorist organization.

As a result, the sale of raw and semi-processed metals, graphite, coal and software for industrial purposes would be subject to sanctions if they were to be used in the Iranian construction sector, the statement said.

In a second resolution, Pompeo specified that four "strategic items" were used in nuclear, military or ballistic missile programs, making trade there subject to sanctions. These materials include stainless steel tubes and magnesium chips.

Reuters says these recent US decisions reflect a drive to increase economic pressure on Iran by putting wider sectors of its economy under sanctions.

In what has been described as an attempt to keep diplomacy open, Washington has allowed foreign companies to continue working on nuclear facilities, making it difficult for Tehran to develop a nuclear weapon.

A source familiar with the matter told Reuters on Thursday that the Ministry of Foreign Affairs has already renewed exemptions for foreign companies for 90 days, including redesigning the Arak reactor to make it unable to produce plutonium purity suitable for bombs under normal operating frequency, as well as the modification of centrifuges at a facility Fordo enrichment in Iran.

The exemptions also include support for the Iranian nuclear reactor at Bushehr, the provision of enriched uranium for the research reactor in Tehran and the transfer of spent nuclear fuel outside Iran.

President Donald Trump's administration last year pulled out of the 2015 nuclear deal under which Iran agreed to curb its nuclear activities in exchange for lifting sanctions that have crippled its economy.

The administration has since reimposed sanctions on Iran, and even tightened it to try to get Tehran to renegotiate a broader agreement that would also limit its ballistic missile program and regional activities.Iran responded by releasing some of its obligations under the agreement until the sanctions were lifted.