Women's right to abortion is under increasing attack behind the former Iron Curtain, a UN-mandated expert group said Tuesday, amid renewed pressure from Catholic groups and falling birth-rates.

"The gap between the eastern part of Europe and the western part of Europe is growing, especially when the issue has to do with abortion," said Wanda Nowicka, a member of a taskforce paving the way for next year's International Conference on Population and Development.

Nowicka, a high-profile reproductive rights campaigner, has since 2011 been deputy speaker of parliament in Poland, a country with one of the most restrictive anti-abortion laws in Europe.

Its abortion law was passed in 1993, four years after the fall of the communist bloc, where liberal abortion laws were commonplace.

The Church, which was a bulwark for the anti-communist opposition in deeply Catholic Poland, was at the forefront of the campaign for change.

Last month, neighbouring Lithuania took a first step towards enacting its own version of the law, giving initial approval to a bill that would prevent terminations except in case of rape, incest or health complications.

Nowicka noted that European Union newcomer Croatia -- like Poland and Lithuania a majority-Catholic nation -- is also weighing up reining in its pro-choice legislation.

Further east, meanwhile, similar moves are afoot in Russia and Ukraine, she said.

"One of the reasons why these countries are moving in this direction is the low birth rate," noted Nowicka.

"This legitimate concern of policymakers over low fertility very often in this part of the world serves as a vehicle to justify considering restrictions to abortion," she said.

Many policymakers in this region think there will be more children if they restrict abortion, she said, adding that data from around the globe disproved that.

"The problem is that this trend seems to be growing," she said.

There has also been debate in Turkey, where abortion has been permitted since the days of the Ottoman Empire.

Last year, Islamist-rooted conservative Prime Minister Tayyip Recep Erdogan provoked outrage among defenders of the pro-choice legal status quo when he likened abortion to murder.

"There's an extensive backlash against sexual health and reproductive rights," said taskforce member Pinar Ilkkaracan, founder of the Turkish group Women for Women's Human Rights.