The US has spent $2.8 trillion (£207 trillion) on counterterrorism efforts since the September 11th attacks, a new report showed.

Washington DC think tank Stimson Center found that over the last nearly 17 years, average spending by the US government on efforts to stem or prevent terrorism was $186.6bn per year. This figure encompassed the continuing war in Afghanistan, the Iraq war, operations in Syria, all homeland security spending within the US, and foreign aid related to counterterrorism.

The spending reached a peak in 2008 at $260bn which roughly accounted for one-fifth of the federal government budget that year. The report indicated that not all of it was necessary either.

The Stimson Center said the bipartisan study “found a variety of weaknesses in definitions, tracking, and consistencies that limit accuracy and contribute to a lack of transparency regarding the current data. These weaknesses make it difficult to evaluate whether [counterterrorism] spending has been effective”.

The report also indicated that the White House Office of Management and Budget’s yearly financial report on homeland security spending was discontinued during the administration of President Donald Trump.

In 2017, the US spent $174bn, or 15 per cent of total federal government spending and an “11-fold increase” from 2001 spending. This is still significantly less than the peak in 2008, but the report indicated that there are no signs counterterrorism funding will decrease any time soon.

Footage shows teenager jailed for terrorism offences at paintball camp where he was training to fight with Isis

“Of $18 trillion in discretionary spending between fiscal years 2002-2017, [counterterrorism] spending made up nearly 16 percent of the whole,” the report said.

“We’re moving in the wrong direction,” said Mike McCord, one of the authors of the Stimson Center report and a former financial officer at the Defence department told the Wall Street Journal.

To provide context as to where funding may better be allocated, the study pointed out that in from 2001 to 2016 “Muslim extremists or jihadis have killed 100 people in the US, or about six per year. In comparison, [opioid overdose] was responsible for more than 20,000 deaths in the US during 2016 alone”.

The 10 developed countries suffering the most deaths from terrorism Show all 10 1 /10 The 10 developed countries suffering the most deaths from terrorism The 10 developed countries suffering the most deaths from terrorism 10: Greece Greek Presidential Guards, or Evzones, take their place for a review by US President Barack Obama and his Greek counterpart Prokopis Pavlopoulos in Athens, Tuesday, Nov. 15, 2016. President Barack Obama arrived in Greece Monday morning on the first stop of his final foreign tour as president, the first visit to Greece by a sitting U.S. president since Bill Clinton in 1999 trip. (AP Photo/Lefteris Pitarakis) AP The 10 developed countries suffering the most deaths from terrorism 9: Denmark Shutterstock The 10 developed countries suffering the most deaths from terrorism 8: Austalia The incident allegedly took place in a primary school in Sydney Getty Images The 10 developed countries suffering the most deaths from terrorism 7: Sweden Ola Ericson/imagebank.sweden.se The 10 developed countries suffering the most deaths from terrorism 6: Mexico People talk to relatives at a section of the wall separating Mexico and the United States, as photographed from Playas Tijuana, in Tijuana, Mexico, November 6, 2016. REUTERS/Stringer FOR EDITORIAL USE ONLY. NO RESALES. NO ARCHIVES. Reuters The 10 developed countries suffering the most deaths from terrorism 5: Germany Afghan asylum seeker Shakira Sarwari, 27, and her two children, Mohammed, 17 months, and Setayesh, 7, are taken off a Munich-bound train in Salzburg, Austria, by German police Anthony Faiola/The Washington Post The 10 developed countries suffering the most deaths from terrorism 4: Israel Israeli Prime Minister Benjamin Netanyahu, attends the weekly cabinet meeting in Jerusalem, Sunday, Nov. 13, 2016. (Ronen Zvulun, Pool via AP) AP The 10 developed countries suffering the most deaths from terrorism 3: US US police have shot 698 people in 2016 so far. Four times more black than white people have been shot Getty The 10 developed countries suffering the most deaths from terrorism 2: France French policemen and security officers stand guard at the entrance of the Bataclan concert hall in Paris on November 12, 2016, a few hours before the reopening concert by British musician Sting to mark the first anniversary of the November 13 Paris attacks. Rock star Sting reopens the Bataclan on November 12, the revered Paris concert hall where jihadists massacred 90 people, with a hugely symbolic show to mark the first anniversary of France's bloodiest terror attacks. Scores of survivors of the Bataclan assault -- the worst of the gun and suicide attacks across the city that night which left 130 dead -- will attend the concert, the dominant event in a weekend of otherwise low-key commemorations. / AFP PHOTO / PHILIPPE LOPEZPHILIPPE LOPEZ/AFP/Getty Images Getty The 10 developed countries suffering the most deaths from terrorism 1: Turkey AP

The study was careful to note that “while the Stimson study group does not take a stance in this debate, it does conclude that arguing either case successfully – that is, determining whether [counterterrorism] expenditures have generated enough benefit to justify their cost – is difficult without accurate information about [said] spending”.

Among the recommendations of the report was for government agencies to develop a consistent and transparent definition of counterterrorism versus war spending.

The centre admitted the report was “imperfect” as a result and because it was not able to account for all foreign aid that may go towards counterterrorism efforts due to the lack of transparent accounting procedures and a set, government-wide definition.