Russia and Israel should not be ruled out as future members of the European Union, senior Liberal Democrat politicians have suggested.

Following this year's expansion of the EU to include new members from central and eastern Europe, the European Commission will shortly be announcing whether Turkey should begin membership negotiations.

Foreign affairs spokesman Sir Menzies Campbell told a conference fringe event on Monday evening that the pool of potential members could be extended further afield.

He told the Centre for Reform think tank organised event that the issue of offering membership to countries across the Mediterranean in north Africa was a "difficult question".

"I don't think there is an easy answer to that," he added.

But with candidate countries required to meet the EU's criteria on human rights, democracy, the rule of law and functioning market economies the north African states were anyway excluded, said Sir Menzies.

"Israel would provide a much more difficult test," he continued, as it was the only democracy in the Middle East.

Taking a different tack, Lib Dem MEP Chris Huhne said membership should be linked to geographic criteria.

"My own view...is that the European Union should only contain countries that at least have a footprint in Europe," he said.

Huhne said it would be "astonishing" to exclude Russia, which has two thirds of its population to the west of the Ural mountains, which are often seen as the geographical boundary of the European continent.

He noted that if Russia did join the EU, the bloc's eastern boundaries would extend almost to Japan.

Both speakers also praised the role of the EU in entrenching democracy and stability in a European continent historically beset by major wars.

"The European Union to my mind is the best guarantee we have that peace will continue," said Huhne.