Ankara (AFP) - The EU's much-hyped deal with Turkey to stem the flow of migrants looked shaky on Friday after Ankara said Brussels had offered too little money and mocked Europe's efforts to tackle the refugee crisis.

Just hours after the European Union announced the accord with great fanfare at a leaders' summit, Ankara said the plan to defuse a crisis that has seen some 600,000 mostly Syrian migrants enter the EU this year was just a draft.

Cracks in the deal emerged as Bulgaria's president apologised after an Afghan refugee was shot dead crossing the border from Turkey.

In the latest in a series of jabs at Europe over the crisis, Turkish President Recep Tayyip Erdogan ridiculed the bloc's efforts to help Syrian refugees.

"They announce they'll take in 30,000 to 40,000 refugees and then they are nominated for the Nobel for that. We are hosting two and a half million refugees but nobody cares," Erdogan said.

The Turkish leader also challenged the EU to take Ankara's bid for EU membership more seriously.

"They keep saying 'We can't do without Turkey.' It's very clear but they are not being clear. Then why don't you let Turkey in the EU?" he asked.

His Foreign Minister Feridun Sinirlioglu heaped scorn on the EU's proposals of financial help, calling the offer "unacceptable" and saying his country needed at least three billion euros ($3.4 bn) in the first year of the deal.

The foreign minister added that the latest action plan is "not final" and merely "a draft on which we are working".

- Bulgaria shooting -

Under the tentative agreement, Turkey had agreed to tackle people smugglers, cooperate with EU border authorities and put a brake on refugees fleeing the Syrian conflict from crossing by sea to Europe.

In exchange, European leaders agreed to speed up easing visa restrictions on Turkish citizens travelling to Europe and give Ankara more funds to tackle the problem.

While they did not specify how much they would give Ankara, they did say the three billion euros demanded by Turkey would be a problem.

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While the summit was underway, the volatile situation on the EU's frontier with Turkey exploded into violence with the fatal Bulgarian border shooting, which the UN refugee agency said was the first of its kind.

The victim was among a group of 54 migrants spotted by a patrol near the southeastern town of Sredets close to the Turkish border and was wounded by a ricochet after border guards fired warning shots into the air, officials said.

The migrants were not armed but they did not obey a police order to stop and put up resistance, they said.

Bulgarian President Rosen Plevneliev said he "deeply regrets" the shooting but said it showed the need for "rapid common European measures to tackle the roots of the crisis."

- Hungary closes Croatia border -

The death adds to the toll of over 3,000 migrants who have died while trying to get to Europe this year, most of them drowning in the Mediterranean.

Interpol on Friday said it would soon launch an operation to improve intelligence sharing on people-smugglers.

The announcement came as Spanish police smashed a network smuggling Moroccans into Spain for 5,000 to 10,000 euros ($5,700-11,400) each.

The migrant crisis, the worst of its kind since World War II, has opened up rifts in the European Union and put unprecedented strain on the right to free circulation that is at the core of the bloc's values.

Just weeks after sealing its border with Serbia with a razor-wire fence, Hungary said it would close its border with Croatia at 2200 GMT on Friday to stem the flow of migrants, blaming the EU summit's failure to push for a bloc-wide frontier guard system.

"After no decision was reached at the EU summit on Thursday on using common EU forces to defend Greece's external border... Hungary has decided to put into operation its border closure," said foreign minister Peter Szijjarto.

Croatian Interior Minister Ranko Ostojic said Zagreb would divert migrants on its territory, who had been planning to travel onto Hungary, towards Slovenia.

"We are turning the route, the corridor towards Slovenia," he told reporters.

Most refugees and migrants are trying to get to Germany, Europe's economic powerhouse, which has said it expects up to one million asylum seekers this year after saying it would open its doors to Syrian refugees.

With many refugees from Syria, Iraq and Eritrea currently failing to lodge asylum request upon arriving in Greece, fearing they will be trapped in the recession-hit country, the European Union's top migration official warned a recent deal to share out refugees in the bloc could flounder.