BRUSSELS (Reuters) - The European Commission delivered a formal warning to the Philippines and Papua New Guinea on Tuesday over illegal fishing, a step that could lead to a ban on exporting to the European Union, the world's biggest fish importer.

The warning, which was welcomed by environmental groups, puts the two countries on the EU's "yellow list", which requires them to improve monitoring and control of fishing practices.

Failure to do so will put them onto the "red list" of nations which are not allowed to sell fish to the 28-nation EU.

"If half of the Western Pacific's tuna is exported to the EU, we cannot ignore illegal fishing activities in this region," European Commissioner for Maritime Affairs and Fisheries Maria Damanaki said in a statement.

The warning follows a thorough analysis and takes into account the countries' development level, the Commission said.

The EU issued similar warnings in 2013 to Curacao, Ghana and South Korea and the Commission is now reviewing whether any of those countries should be red-listed or whether they have improved enough to be taken off the yellow list.

Campaign groups the Environmental Justice Foundation, Oceana, The Pew Charitable Trusts and WWF welcomed the EU's latest move, saying that illegal fishing accounted for around one in five wild-caught marine fish, a haul worth up to 17 billion euros ($23 billion) per year.

The EU has banned fish imports from Cambodia, Belize and Guinea over illegal fishing, and EU fishing vessels are not allowed to operate in those countries' coastal waters.

($1 = 0.7332 Euros)


(Reporting by Barbara Lewis; Editing by Gareth Jones)