Two Americans were refused to enter Israel in the Ben-Gurion International Airport early Friday morning, with hundreds of participants of a pro-Palestinian fly-in campaign having been blocked from boarding the flights to Israel during the past two days.

The Israel Police at Ben-Gurion International Airport deported two American tourists wearing "fly-in" T-shirts arriving on a flight from Greece, sending them back to Athens on the next flight, Police spokesman Mickey Rosenfeld told Xinhua.

Officials ratcheted down visible security at the airport a notch overnight Thursday, after Israel gave foreign carriers a blacklist of close to 400 suspected pro-Palestinian activists headed here on flights from European airports.

"Due to statements of pro-Palestinian radicals to arrive on commercial flights from abroad to disrupt the order and confront security forces at friction points, it was decided to refuse their entry in accordance with our authority according to the Law of Entry to Israel 1952," the letter read.

"In light of the above-mentioned, you are required not to board them on your flights to Israel. Failure to comply with this directive would result in a delay on the flight and their return on the same flight," the warning read, according to The Jerusalem Post.

A police spokesman told local news site Ynet that the foreign airlines have stopped about 200 activists from boarding flights.

A group of some 50 protesters demonstrated at Paris' Charles De Gaulle Airport on Friday, saying that Israel had "occupied" the facility.

Organizers of the "Welcome Palestine" organization, which says it numbers some 40 groups, said earlier in the week that hundreds of mostly European activists were planning to fly to Israel on Friday, in order to take part in events in the West Bank.

"They are coming in peace without any violent attitude towards Israel," and they will participate in cultural activities and trips if managing to reach the West Bank, Mazen Qumsiyeh, one of the organizers told Xinhua.

The organizers issued a statement on Friday, accusing Israel's denial of entrance to international visitors illegal and saying that the "Welcome to Palestine" campaign has been successful in the sense of "exposing Israeli attempts to isolate Palestinians."

The organizers will announce their further plan later in the day, according to the statement sent to Xinhua.

Meanwhile, back in the Ben-Gurion arrivals hall, groups of uniformed police and airport security meandered among the crowds of visitors as they rolled luggage carts into the hall, after clearing passport control and customs.

Police briefly detained and then released three French teenagers draped in Israel-flags, who had chanted pro-Israel slogans. The police warned them not to behave in any manner that would disturb passengers passing through the arrivals hall, or airport operations.

Dozens of news crew toting video cameras and microphones buttonholed arrivals, asking if they'd encountered any signs of tension or heightened security at the departure airports.

Late Thursday night, Rosenfeld said "there were no problems with the passengers on two flights, from France and Germany," that he accompanied from their exit from the airplane, through customs, and into the arrivals hall.

"This event will end with either no problems or as a catastrophe. There will not be a middle-ground," a senior airport official told Ha'aretz.

Passengers on flights from Cyprus and Germany told Xinhua that they did not see any heightened security surrounding their departure on during the flights.

Israeli officials on Friday said they'd renew their elevated security stance, Army Radio reported, including at the entrance to the airport's vehicular security checkpoint, far from the terminal, where activists might send buses of protesters.

Israel has slammed the activists' attempts to enter its territory under the rubric of the "Welcome Palestine," events in taking place at locations within its territory and in the West Bank protesting Israel's policies, and consider it an affront to their sovereignty.

"Every country has the basic right to prevent the infiltration of provocateurs into its territory," Israeli Prime Minister Benjamin Netanyahu said on Wednesday at a press conference with Bulgarian Prime Minister Boyko Borisov, held in Sofia.

Hundreds of more pro-Palestinian activists are still expected to arrive in the Ben-Gurion airport on Friday as the "Welcome Palestine" campaign organizers said earlier in the week that around 600 to 800 people had been planning to fly to the airport.

Israeli Public Security Minister Yitzhak Aharonovitch, at an assessing meeting together with police and other officials in the airport Friday morning, has instructed the security forces continue to deploy in the airport so as to be able to deal with incoming flights this afternoon, according to a statement by Israeli government.