BRUSSELS - In what officials acknowledge is a symbolic gesture, three passenger flights were allowed to plan to take off from Brussels Airport in Zaventem on Sunday after a 12-day shutdown caused by a deadly bombing attack.

Arnaud Feist, the CEO of Brussels Airport Co., says the Brussels Airlines flights to Athens, Turin in Italy and Faro in Portugal were "a sign of hope" and a demonstration of "shared will" that even partial passenger service could resume so soon following "the darkest days in the history of aviation in Belgium."

The airport has been closed since two devastating suicide bombings on March 22 in its main terminal and one in a Brussels subway train killed 32 victims and wounded 270. The attacks were claimed by the Islamic State of Iraq and Syria (ISIS.)

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Feist said Belgium's biggest airport should be back at around 20 percent of capacity on Monday and able to process 800 passengers an hour. Speaking at a news conference Saturday, he hoped that full service at the airport could be restored by the end of June or the beginning of July in time for the summer vacation season.

Prior to the attacks, the key European aviation hub usually handled about 600 flights a day. It served 1.5 million passengers in February.

New security measures have been ordered at the airport to minimize the chances of any repeat attacks.

Police on Sunday were conducting spot checks of vehicles before they arrive, and a large white tent was set up outside the terminal to screen IDs and travel documents before allowing anyone to enter the building. A drop-off parking area outside the terminal has been closed. There will be no access by rail or public transport to the airport for the foreseeable future.

The bombers entered the check-in area with suitcases packed with explosives and nails, and the resulting blasts collapsed the ceiling and shattered windows in addition to killing 16 people.

The attacks have prompted a wider discussion among aviation authorities in many countries over whether to impose routine security checks at the entry to airport terminals

Until the terminal can be fully repaired, Feist said departing passengers will first enter a temporary structure erected on the tarmac, then go to a specially built check-in area.

There will be no access by rail or public transport to the airport for the foreseeable future, he said.

Delta, meanwhile, said it was suspending service between Atlanta and Brussels until March 2017 due to the continued uncertainty surrounding the airport's re-opening and weakening demand. It still plans to resume service between New York's John F. Kennedy Airport and Brussels once the Brussels Airport provides clearance.