The UK communications giant, BT, is facing a government investigation for allegedly aiding lethal and illegal US drone strikes in Yemen and Somalia.

The human rights group, Reprieve, has lodged a formal complaint with the UK Government against the company, arguing that it has breached guidelines on responsible business behaviour drawn up by the 34-country Organisation for Economic Co-operation and Development (OECD).

Reprieve has obtained details of a $23 million deal agreed last September between BT and the US government's Defense Information Systems Agency to connect the US drone base at Camp Lemonnier in African republic Djibouti by fibre-optic cable to RAF Croughton in Northamptonshire, which serves as a major US communications base.

Lemonnier is the main centre for US drone operations outside Afghanistan. It sends Predator and Reaper unmanned aerial vehicles armed with Hellfire missiles on "targeted killing" missions against suspected terrorist cells in Yemen and Somalia.

But Reprieve says the attacks violate international law because they are carried out in areas where no war has been declared. In January, the United Nations launched an investigation into the legality and casualties of the strikes, headed by the special rapporteur on human rights and counter-terrorism, British barrister Ben Emmerson QC.

According to the Bureau of Investigative Journalism at City University in London, confirmed drone strikes in Yemen have killed between 240 and 349 people since 2002, with a further 283-456 left dead by "possible" strikes. Between 37 and 97 of those killed were said to be civilians, up to 11 of them children.

There is less information available for Somalia where, since 2007, up to 27 people have been reported killed by drones, maybe 15 of them civilians. Because the operations are shrouded in secrecy, it is difficult to be certain of the exact death toll.

Reprieve's complaint alleges that BT, which held its annual general meeting in Edinburgh last week, has flouted human rights provisions in the OECD guidelines on multinational enterprises. Under the published procedures, BT will now be asked for a response, and an initial assessment of the complaint will be made.

The OECD guidelines require companies to "respect the internationally recognised human rights of those affected by their activities". Companies should "seek ways to prevent or mitigate adverse human rights impacts that are directly linked to their business operations, products or services by a business relationship, even if they do not contribute to these impacts."

Drones have "devastating human rights impacts" on communities in Yemen which are unable to protect themselves and their families, Reprieve says. "BT has contributed to the large-scale human rights violations caused by the US use of drones in Yemen."

Reprieve's lawyer, Catherine Gilfedder, argued that Yemeni civilians were victims of "brutal violations" from the drone attacks. "The US's secretive and illegal campaign of drone strikes in Yemen is killing civilians and traumatising communities, yet it remains largely hidden from the eyes of the world," she told the Sunday Herald.

She called on BT to come clean over its involvement in the strikes, adding: "Its management cannot continue to bury their heads in the sand on this issue, especially if they want to maintain BT's reputation as a responsible company."

When Reprieve asked BT about its US defence contract, the company refused to discuss it. "BT does not disclose contractual matters," wrote Prakash Mistry from the company's legal department.

The campaign group then approached BT's chief executive, Ian Livingston, who is about to leave to become a UK Government trade minister. "BT have clear policies regarding responsible business and we are satisfied that our contracts are consistent with them," he said.

When asked to comment by the Sunday Herald, BT pointed out that it provided communications for governments and thousands of organisations around the world. "We are comfortable having the US government as a client," a company spokesman said.

Green MSP Alison Johnstone urged the UK Government to assess Reprieve's complaint. "There's a lot of public unease over drones," she said. "The idea of a British organisation profiting while alleged human rights abuses are taking place raises many questions. Did the UK authorities know about this contract and, if so, did they express any concerns?"

The US Defense Information Systems Agency did not respond to a request to comment. But in a speech in Washington DC on May 23, President Barack Obama accepted that drones had killed and injured civilians. "It is a hard fact that US strikes have resulted in civilian casualties, a risk that exists in every war," he said. "And for the families of those civilians, no words or legal construct can justify their loss."

Nevertheless, he argued that drones were used legally, proportionately and in self-defence to prevent future terrorist attacks. "Simply put, these strikes have saved lives," he said. "Remember that the terrorists we are after target civilians, and the death toll from their acts of terrorism against Muslims dwarfs any estimate of civilian casualties from drone strikes."

While Obama insisted on better oversight of drones strikes he defended their use as part of a "just war" on terrorism. "Yes, the conflict with al-Qaeda, like all armed conflict, invites tragedy," he said. "But by narrowly targeting our action against those who want to kill us and not the people they hide among, we are choosing the course of action least likely to result in the loss of innocent life.