The EU will open new membership talks with Turkey as planned in a few days, EU diplomatic sources said Wednesday, just as Ankara's accession becomes a hot-button issue in Britain's vote on its future in the bloc.

One source, who asked not to be named, told AFP that EU member states will meet June 30 to agree to open a new negotiating chapter with Turkey on finance and budget affairs.

A British spokesperson in Brussels said the decision was procedural and followed up a pledge made by European Union leaders in March to open another accession chapter with Turkey.

"In March, all member states agreed to open Chapter 33, during the Netherlands (six-month EU) presidency. This is a technical step to implement that agreement," the spokesperson said.

EU leaders at a summit in March agree to speed up Turkey's long-stalled membership talks as part of an accord with Ankara on tackling the migration crisis, promising to open at least one new chapter by the end of June when the Netherlands presidency finishes.

The issue however has become caught up in the campaign for Thursday's bitterly-fought Brexit referendum amid charges by the "Leave" camp that accession will allow millions of Turks into the country.

British Prime Minister David Cameron insists Turkey will not join the 28-nation bloc for many years, even though the government's official position is to support Ankara's membership.

Since Muslim-majority Turkey formally launched its membership bid in 2005, the EU has opened 15 chapters out of the 35 required to join the bloc.

So far only one chapter has been completed, with disagreements over Turkey's human rights record an obstacle for many EU states.

Under the March accord, the EU also agreed to boost aid to Turkey to cope with millions of refugees, mostly Syrians, on its territory and to speed up visa liberalisation.