Seventeen Iranians have been charged with allegedly conducting a years-long "co-ordinated campaign" of cyber attacks in an effort to steal data from US organisations.

The US Department of Justice (DoJ) said members of the Iran-based Mabna Institute had targeted the computer systems of 144 American universities and 42 private sector firms since at least 2013.

The group is alleged to have stolen more than 31 terabytes of academic data and intellectual property worth approximately $3.4bn (£2.5m) over the course of the "massive" campaign, the DoJ said.

FBI Assistant Director in Charge James C Barnacle, Jr described the coordinated cyber attacks as "a serious threat to our national security".

Many of the attacks were conducted on behalf of Iran's Islamic Revolutionary Guard Corps (IRGC), the DoJ said in a statement, as well as for "other Iranian government and university clients".

"Backed by the IRGC, this operation reflects a broader, organised effort to target US institutions and global partners," Barnacle said.

The DoJ said Mabna had targeted the accounts of 100,000 academics around the world and successfully compromised 8,000 professors' email accounts at 144 US-based universities and another 178 academic institutions internationally.

The campaign started in approximately 2013 and continued until at least December 2017, the DoJ added.

The department also announced it was offering a $10m (£7.3m) reward for information leading to the location of five of the alleged hackers-for-hire who have been charged.

US Attorney for the Southern District of New York Jamie McDonald said cyber operations have "become a central instrument of national power", warning of the dangerous impact cyber attacks have on US security and the economy.

In addition to academic institutions, Mabna is alleged to have targeted and compromised employee email accounts from at least five US federal and state government agencies.

At least 42 US-based private companies and 11 foreign companies based in Germany, Italy, Switzerland, Sweden, and the UK were also targeted, the DoJ said.

The Mabna Institute was founded in 2013 to assist Iranian academic organisations in "stealing access to non-Iranian scientific resources", according to the DoJ.

Nine of the 17 members charged on Tuesday were previously charged in a seven-count indictment in March 2018.