BRUSSELS (Reuters) - The European Union is considering giving a new EU border force powers to intervene and guard a member state’s external frontier to protect the Schengen open-borders zone, EU officials and diplomats said on Friday.

A barbed wire is seen in front of a European Union flag at an immigration reception centre in Bicske, Hungary June 25, 2015. REUTERS/Laszlo Balogh

Such a move might be blocked by states wary of surrendering sovereign control of their territory. But the discussion reflects fears that Greece’s failure to manage a flood of migrants from Turkey has brought Schengen’s system of open borders to the brink of collapse.

Germany’s Thomas de Maiziere, in Brussels for a meeting of EU interior ministers, said he expected a proposal from the EU executive due on Dec. 15 to include giving responsibility for controlling a frontier with a non-Schengen country to Frontex, the EU’s border agency, if a member state failed to do so.

“The Commission should put forward a proposal ... which has the goal of when a national state is not effectively fulfilling its duty of defending the external border, then that can be taken over by Frontex,” de Maiziere told reporters.

He noted a Franco-German push for Frontex, whose role is largely to coordinate national border agencies, to be complemented by a permanent European Border and Coast Guard -- a measure the European Commission will propose on Dec.15.

Greece has come under heavy pressure from states concerned about Schengen this week to accept EU offers of help on its borders. Diplomats have warned that Athens might find itself effectively excluded from the Schengen zone if it failed to work with other Europeans to control migration.

On Thursday, Greece finally agreed to accept help from Frontex, averting a showdown at the ministerial meeting in Brussels.

After threatening Greece with triggering rules allowing for internal border controls within Schengen for up to two years, the ministers meeting in Brussels on Friday have not asked the bloc’s executive arm to activate the procedure.

“It is not legally possible to exclude a state from the Schengen area. We cannot expel or exclude a member state from the Schengen area... We weren’t targeting any country in the north or the south or the center,” said Jean Asselborn, the minister of foreign affairs and migration of Luxembourg, which first tabled a paper invoking the two-year rule.

NEW EU BORDER FORCE

EU diplomats said the proposals due on Dec.15 to bolster defense of the external Schengen frontiers would look at whether the EU must rely on an invitation from the state concerned.

“One option could be not to seek the member state’s approval for deploying Frontex but activating it by a majority vote among all 28 members,” an EU official said.

Under the Schengen Borders Code, the Commission can now recommend a state accept help from other EU members to control its frontiers. But it cannot force it to accept help, something that may in any case not be practicable.

The code also gives states the right to impose controls on internal Schengen borders if external borders are neglected. As Greece has no land border with the rest of the Schengen zone, that could mean obliging ferries and flights coming from Greece to undergo passport checks.

Asked whether an EU force should require an invitation or could be imposed by the bloc, Swedish Interior Minister Anders Ygeman said: “Border control is the competence for the member states, and it’s hard to say that there is a need to impose that on member states forcefully.

“On the other hand,” he said, referring to this week’s pressure on Greece, “we must safeguard the borders of Schengen and what we have seen is that if a country is not able to protect its own border, it can leave Schengen or accept Frontex. It’s not mandatory, but in practice it’s quite mandatory.”

Ministers and the Commission welcomed Greece’s decision on Thursday to accept more help from Frontex.

“Greece is finally taking responsibility for guarding the external European border,” Austrian Interior Minister Johanna Mikl-Leitner said. “I have for months been demanding that Greece must recognize this responsibility and be ready to accept European help. This is an important step in the right direction.”

A dramatic increase in EU powers over national territory would be deeply controversial in much of Europe. On Thursday, Danes, who are part of the Schengen zone, heeded Eurosceptic calls and voted against giving their government power to deepen its cooperation with the EU police agency.

The European Union faces another test over the next two years as Britain, its second biggest economy, prepares to hold a referendum on whether to quit. Although not a member of the 26-nation Schengen zone, and so unaffected by increased powers for EU border guards, increasing Brussels’s say over security policies in Schengen states might fuel the campaign to leave.