* Israel says it will deport pro-Palestinian activists
* Hundreds of police deployed at Tel Aviv airport (Adds Netanyahu remarks, details, violence in West Bank)
JERUSALEM, April 15 (Reuters) - More than 40 pro-Palestinian activists reached Tel Aviv's international airport on Sunday as part of an attempted "fly-in", only to be detained as Israel denied them entry and scrambled to stop other campaigners boarding flights in Europe.
Israel's decision to distribute "no-fly" lists to European carriers and deploy hundreds of police at Ben Gurion airport underlined its deep concern over international campaigns against its treatment of the Palestinians.
Police spokesman Micky Rosenfeld said that 45 people had been refused entry at Ben Gurion airport by the evening and would be deported.
Nine Israeli supporters, some holding "Welcome to Palestine" signs, were also detained as they waited to greet the arrivals.
An Interior Ministry spokeswoman said Israel on Wednesday had given airlines the names of some 1,200 activists whose entry would be barred. Israel made it clear the carriers would have to bear the costs of repatriating any deportees.
Leehee Rothschild, a "Welcome to Palestine" activist, said dozens of campaigners had since been informed by airlines that their tickets to Tel Aviv had been cancelled.
Organisers had said some 1,200 Palestinian supporters throughout Europe had bought plane tickets to Israel, planning to travel on to the occupied West Bank, an hour's drive from Tel Aviv, as part of a campaign called "Welcome to Palestine".
The aim of the so-called "flytilla", organisers said, was to help open an international school and a museum in Bethlehem.
But Israel, which described the fly-in as a misguided protest against "the Middle East's sole democracy", denounced the activists as provocateurs and said it would deny entry to anyone who threatened public order.
"What are they doing here? ... If they want to check the issue of human rights, they should go to Syria, maybe they can help stop the slaughter of thousands of innocents. They should go to Iran and stop the stoning of women," Prime Minister Netanyahu told reporters on Sunday.
In a separate incident in the West Bank, video footage broadcast on Sunday of pro-Palestinian protestors confronting Israeli soldiers a day earlier showed an Israeli Lieutenant Colonel smacking an activist in the face with his rifle.
The Israeli military called it "a serious incident" and a spokeswoman said it was investigating what happened and would take the appropriate steps.
In Brussels' Zaventem airport, around 100 Belgian and French activists were not allowed to board flights to Israel. T hirteen people were blocked from a flight in Manchester.
The activists, some of whom said they wanted to build a new school, held up letters that were handed to them at the airport which said they were on a no-fly list because they intended to "disrupt order and confront security forces at friction points".
Cellphone video uploaded by an activist to the internet showed about 20 pro-Palestinian activists at Charles de Gaulle airport in Paris surrounded by police.
Some Israeli political commentators said Israeli authorities had over-reacted, playing into the hands of pro-Palestinian campaigners seeking publicity.
A similar, though smaller event last year led to a few hundred activists being blocked at European airports and more than 100 others were deported after Israel denied them entry.
"Israel's willingness to detain people who have not committed any crime and have done nothing but say they came to visit Palestine is a hysterical reaction," Rothschild said.
Palestinians hope to establish a state in the West Bank and East Jerusalem, areas Israel captured in the 1967 Middle East War, and the Gaza Strip that is ruled by Islamist group Hamas.
Netanyahu's office released a letter on Saturday which it hoped to hand the activists upon their arrival.
Echoing the "thank you for choosing our airline" announcements cabin crew often make to passengers after landing, the letter said: "We appreciate your choosing to make Israel the object of your humanitarian concerns."
It called the activists' campaign misguided and said they could have chosen instead "to protest (against) the Syrian regime's daily savagery against its own people".
Israel's left-wing Haaretz newspaper, criticising the government's ban, said it should invite "peace activists to visit anywhere and welcome them with flowers". (Additional reporting by Claire Davenport in Brussels; Editing by Jon Hemming and Andrew Osborn)