Berlin's biggest universities have warned that they will end their contracts with Elsevier in a further escalation of a dispute between German research institutions and the publisher.

In order to increase pressure on Elsevier to agree to a new nationwide deal, the Free, Humboldt and Technical universities of Berlin, as well as Charité - Universitätsmedizin Berlin, announced they would not extend their current contracts beyond the end of 2017.

More than 70 research organisations in Germany are already without Elsevier contracts, and in 2018 the Berlin universities will join their ranks.

German universities, research organisations such as the Max Planck society and the German Research Foundation have clubbed together to demand a better deal from Elsevier, including blanket open access rights for published articles and a reduction in costs.

But negotiations broke down at the end of 2016, with a fundamental issue dividing the two sides: the German side wants to be able to subtract open access article processing charges from journal subscription fees, but Elsevier wants to keep these parts of its business separate. In February, Elsevier restored access to Germany's research institutions, even though no deal has yet been agreed.

In a statement, Elsevier said it was "working diligently to find a mutually acceptable solution" to the standoff.

"Elsevier agrees with all of HRK's [Hochschulrektorenkonferenz, Germany's organisation of university leaders] basic requests for a national license and open access, and this is reflected in the numerous constructive proposals that we have submitted to HRK," the statement continues.

But it accused the HRK of "unilaterally" cancelling a discussion workshop scheduled for this week in a move it called "disappointing and concerning".

Previously, Horst Hippler, president of the HRK, warned Elsevier that "there can be no mistaking how serious we are about this".

"Today, expenditure on the three major publishers Elsevier, Springer Nature and Wiley is already tying up a major part of scientific libraries' acquisition budgets – and rising," he said. "This cannot continue."

david.matthews@timeshighereducation.com