Macedonia sent back hundreds of refugees to Greece on Tuesday, a day after they bypassed a border fence in a mass push to continue their journey north to Europe's prosperous heartland — a move Greece blamed on "criminal misinformation" possibly spread by volunteers working with them.

Interior Ministry spokesman Toni Angelovski told The Associated Press the migrants "have been returned to Greece."

About 1,500 people, frustrated at being stuck for weeks in a waterlogged tent city outside the closed crossing of Idomeni, pushed their way into Macedonia on Monday through an unguarded section of the border. They walked about 5 kilometers (3 miles) and forded a swollen stream near the Greek village of Hamilo.

A Macedonian official said 700 migrants who had been detained overnight were deported to Greece through the same location they entered. The official, who spoke on condition of anonymity because he was not authorized to discuss the matter with the press, also said about 50 journalists and volunteers detained with the migrants were released after paying fines of 250 euros ($280) for illegally entering Macedonia.

Greek police said groups of migrants were seen coming back to Greece from unguarded sections of the border east and west of Idomeni — although Greece says it received no official notification or repatriation request from Macedonia. A spokesman for the United Nations refugee agency in Idomeni, Babar Baloch, confirmed that many had returned to Idomeni.

About 200 people who had camped overnight near Hamilo went back to Idomeni on Tuesday, while Macedonian police guarded the area. It was not possible to account for all the migrants.

Despite repeated Greek appeals for them to move to available organized shelters, about 14,000 people are stuck in the Idomeni tent city in swampy conditions after days of heavy rain, and hundreds were queuing under a shelter Tuesday for food handouts.

"As long as (refugees) still believe that there is a chance of getting through (to Macedonia), this will continue," Immigration Minister Ioannis Mouzalas said. "There is no way the border will open."

For months, hundreds of thousands of people from the Middle East and Africa flowed through Idomeni, on their way to seek asylum in central Europe. But a tightening in border controls that started in Austria and extended down the Balkan migration route ended in a total border closure last week. Now, about 44,000 people are stranded in Greece, after crossing from nearby Turkey in flimsy smugglers' boats.

The European Union's commissioner for migration, Dimitris Avramopoulos — a Greek politician — visited Idomeni Tuesday and deplored the "tragic, unacceptable" conditions he saw.

"This tests the principles and values of the civilized world, and Europe," he said. "This situation must end immediately."

Avramopoulos also appealed to EU countries to honor the bloc's commitments to share out asylum-seekers.

Greek Prime Minister Alexis Tsipras blamed Monday's mass move to circumvent the border fence on misleading leaflets distributed at Idomeni, which encouraged the refugees to make a concerted push north.

Tsipras said "unknown people, perhaps groups that call themselves volunteers," handed out leaflets advising migrants to cross the border by bypassing the fence and warning that if migrants left the overflowing Idomeni camp for shelters in northern Greece, they would be imprisoned there.

"This is criminal behavior toward people who face great hardship," Tsipras said. "This must stop."

Greek police are investigating the incident.

Tsipras urged the refugees to leave Idomeni for the shelters, and called on volunteers working with them to help scotch false rumors.

Macedonian Foreign Minister Nikola Poposki, in a statement, said only a "united and humane" response from the European Union can solve the continent's migration problem.

"More migrants in deteriorating tent cities at the border only encourages (people) smuggling," Poposki said.