By Gabriela Baczynska

BRUSSELS (Reuters) - The European Union's executive said on Wednesday that emergency border checks introduced within Europe's passport-free travel zone by countries including Germany and Sweden to stem a migrant influx were still justified even though arrival numbers have eased.

In a blow to European integration, the EU partly suspended the Schengen Area arrangement as member states were overwhelmed by the arrival of some 1.3 million refugees and migrants in 2015.

"The border controls have been necessary," said EU Migration Commissioner Dimitris Avramopoulos. "The current controls remain within the conditions set by the Schengen rules."

He said, however, this did not mean the five states - which also include Norway, Denmark and Austria - would necessarily be allowed to extend the extraordinary measures once they expire on Nov. 12.

He said 5,651 people have now been moved to other member states from Italy and Greece, the main gateways to Europe for people fleeing wars and poverty in the Middle East and Africa.

Most of those who reached the bloc last year made their way north to Germany and other wealthy EU states, triggering bitter political rows within the union, which is also struggling with weak economic growth and Britain's vote to leave.

Avramopoulos said more than 60,000 people were still stuck in Greece. Although conditions there had improved, he said Athens had to upgrade reception facilities and access to asylum, and boost protection for unaccompanied children.

Vincent Cochetel, head of the European bureau of the U.N. refugee agency told a separate briefing in Brussels on Wednesday that the situation on the Greek islands was "dire".

"The centres were never meant to accommodate so many people, processing has been slow... the fact that a large number of people on the islands are not processed is creating tension on a daily basis," he said.

"FLEXIBLE SOLIDARITY"

The number of people relocated is far fewer than the 160,000 people who were meant to be shared out among EU states. Poland, Hungary and other eastern members have refused to take part and even launched legal cases against the bloc's quota system.

Avramopoulos, who praised Germany and Belgium for taking people in, said he hoped some 30,000 more would be transferred from Greece within a year.

But with relocation failing to progress on a large scale and with the eastern nations refusing to budge, Brussels now says Warsaw, Budapest, Prague and Bratislava would increasingly be allowed to help the bloc's migration efforts in different ways.

They have suggested that out of "flexible solidarity", they could send more guards or equipment to protect the EU's external frontier, offseting their refusal to accommodate refugees on their own soil.

Berlin and others are not pleased but accept that relocation has proven very divisive at a time when the bloc is desperate for unity after Britain's vote to leave the EU.

"We need to bring all on board," said one EU official.

Avramopoulos also said a migration deal with Turkey, though heavily criticised by rights groups for undermining refugees' rights, was keeping arrivals low, with average figures at 85 people a day in Greece since June.

That compares with more than 1,700 per day before the Turkey deal was implemented and 7,000 per day in October 2015, he said.

The EU is working on visa liberalisation for Turkey in exchange for Ankara's help on migration, but major hurdles remain. The Commission said it was still seeking "legislative and procedural changes" to Turkey's anti-terror laws.

Asked if the different EU measures to stem immigration meant there would not be a repeat of the chaos of 2015, Avramopoulos said: "Yes, we are better prepared than before. Europe will not be caught by surprise again."

(Additional reporting by Marilyn Haigh, writing by Gabriela Baczynska, editing by Raissa Kasolowsky and Hugh Lawson)