Greek officials fumbled their response to a minor oil spill that is now threatening beaches near Athens five days after the suspicious sinking of a tanker, environmental groups said Thursday.

"This leak happened near the country's biggest harbour, just miles away from the operation centre of the ministry tasked with addressing such disasters," Dimitris Ibrahim, campaign director at Greenpeace Greece, told news portal in.gr.

Adding insult to injury, the amount of oil in question was "relatively small," Ibrahim said.

The oil spill on Sunday compromised beaches on the island of Salamis and officials were confident that it could be contained given mild wind conditions.

But by Thursday, parts of the slick had drifted miles away to the Athens coastal resort of Glyfada and was threatening the popular beaches of Voula and Vouliagmeni.

WWF Greece was likewise incredulous that "a country with heavy tankers traffic has proven unable to protect its beaches from an initially small-scale incident."

"Nobody thought the slick would reach us," Glyfada mayor Yiorgos Papanikolaou told Skai TV.

"If someone had warned us even on Tuesday, we would have taken precautions," said Papanikolaou.

"We must act quickly to prevent long-term damage,"

Mayors across the coast have issued beach warnings and fishermen have been advised to avoid the area at present.

Merchant marine minister Panagiotis Kouroublis, who was attending a shipping conference in London -- and is under fire for not interrupting the trip -- is visiting the area on Thursday.

He insists that every available resource has been thrown at the oil slick.

"A giant operation is under way," he told state agency ANA. "Everything will be clean in 20-25 days."

The European Union has contributed an anti-pollution ship.

The 45-year-old vessel Agia Zoni II sank on Sunday near the island of Salamis while under anchor. The cause is still unknown.

The Greek-flagged tanker was carrying around 2,500 tonnes of fuel.

The only people on board at the time, the tanker's captain and chief engineer, were charged with negligence and released pending trial.

The ship's owners said the tanker was fully seaworthy and all its documentation was in order.

An operation is under way to drain the fuel remaining on board.

Source: AFP