BRUSSELS (Reuters) - The European Union executive is considering whether to make United States and Canadian citizens apply for visas before travelling to the bloc, in a move that could raise tensions as Brussels negotiates a free trade pact with Washington.

The European Commission will debate the issue, prompted by US and Canadian refusals to waive their visa requirements for holders of some EU member states' passports, at a meeting next Tuesday.

That is just over a week before US President Barack Obama arrives in Europe on a visit that will include discussions on trade.

"A political debate and decision is obviously needed on such an important issue. But there is a real risk that the EU would move towards visas for the two," an EU source said.

Washington and Ottawa both demand visas before travelling for Romanians and Bulgarians, whose states joined the EU in 2007. The United States also excludes Croatians, Cypriots and Poles from a visa waiver scheme offered to other EU citizens.

Europe's Schengen area, comprising 26 states, most of which are in the 28-member EU, has a common visa system. Poland is a member of Schengen, and the other four states are due to join.

Trade negotiations between Brussels and Washington are at a crucial point since both sides believe their transatlantic agreement, known as TTIP, stands a better chance of passing before President Barack Obama leaves the White House in January.

Mr Obama is due to visit Britain before meeting German Chancellor Angela Merkel at a trade fair in Hanover on April 24.