It began calmly enough with a march down the high street after midday prayers at the mosque. Palestinian villagers were surrounded by dozens of foreigners singing and waving flags. They turned and headed out to the olive-tree fields and up towards the broad path of Israel's West Bank barrier. There, behind a concrete hilltop bunker, the Israeli soldiers looked down on them.

The crowd approached the barrier, still singing. One man flew a paper kite shaped as a plane. "This land is a closed military zone," an Israeli soldier shouted in flawless Arabic over a loudspeaker. "You are not allowed near the wall." Then the soldiers fired a barrage of teargas.

It has been like this every Friday in the village of Bil'in for more than four years – the most persistent popular demonstration against Israel's vast steel and concrete barrier. It is a protest founded on non-violence that is spreading to other West Bank villages. But it has become increasingly dangerous.

On April 17, on the hillside at Bil'in, a Palestinian named Basem Abu Rahmeh, 31, was shot with a high-velocity Israeli teargas canister that sliced a hole into his chest, caused massive internal bleeding and quickly killed him. Video footage shot by another demonstrator shows he was unarmed, many metres from the barrier and posing no threat to the soldiers.

The Israeli military said it faced a "violent and illegal riot" and is investigating. On Friday the demonstrators at Bil'in wore Rameh's image on T-shirts and carried it on posters.

Last month another demonstrator, an American named Tristan Anderson, 38, was hit in the head by an identical high-velocity teargas canister in a protest against the barrier at the nearby village of Na'alin. He was severely injured, losing the sight in his right eye and suffering brain damage. "To shoot peaceful demonstrators is really horrifying to us," said his mother, Nancy.

Friday's demonstration lasted around three hours. The crowd repeatedly surged towards the fence, then retreated under clouds of teargas. The military sounded a constant, high-pitched siren, interspersed with warnings in Arabic and Hebrew: "Go back. You with the flag, go back" and, incongruously, in English: "You are entering a naval vessel exclusion zone. Reverse course immediately."

The Bil'in demonstration was always intended to be non-violent, although on Friday, as is often the case, there were half a dozen younger, angrier men lobbing stones at the soldiers with slingshots. The Israeli military, for its part, fires teargas, stun grenades, rubber-coated bullets and sometimes live ammunition at the crowd.

There have long been Palestinian advocates of non-violence, but they were drowned out by the militancy of the second intifada, the uprising that began in late 2000 and erupted into waves of appalling suicide bombings.

Eyad Burnat, 36, has spent long hours in discussions with the young men of Bil'in, a small village of fewer than 2,000, convincing them of the merits of "civil grassroots resistance".

"Of course it gets more difficult when someone is killed," said Burnat, who heads the demonstration. "But we've faced these problems in the past. We've had more than 60 people arrested and still they go back to non-violence. We've made a strategic decision."

Some, like the moderate Palestinian MP Mustafa Barghouti, hope this might be the start of a broader movement throughout Palestinian society. "It is a spark that is spreading," he said in Bil'in. "It gives an alternative to the useless negotiations and to those who say only violence can help."

But it is not so much that all the young men of the village are converted to the peaceful cause, rather that they respect and follow their elders. "I personally don't believe in non-violent resistance," said Nayef al-Khatib, 21, an accountancy student. "They've taken our land by force so we should take it back from them by force."

The barrier at Bil'in cuts off the village from more than half its agricultural land and has allowed the continuing expansion of Jewish settlements, including the vast, ultra-Orthodox settlement of Modiin Illit, even though all settlements on occupied land are illegal under international law.

The international court of justice said in a 2004 advisory opinion that the barrier was illegal where it crossed into the West Bank, and even Israel's supreme court ruled nearly two years ago that the route at Bil'in did not conform to any "security-military reasons" and must be changed. But it has not been moved.

Like most of the men in the village, Nayef al-Khatib has spent time in jail. He was arrested aged 17 for demonstrating and spent a year behind bars, taking his final year of high school from his prison cell. That jail term means he cannot now obtain a permit to travel to Jerusalem or across to Jordan and is often held for hours at Israeli military checkpoints inside the West Bank. "But it was an honour for me. Now I'm like the older men," he said.

Some of those older men are influential. Ahmad al-Khatib, 32, was once a member of the al-Aqsa Martyrs' Brigade, a prominent militant group, and was jailed for a year for transporting weapons. Now he is committed to non-violence, even objecting to the stone throwers.

"I don't apologise for what I did, but I'm not going back to it," he said. "We are an occupied nation according to international law and we have the right to resist, though that doesn't mean I support suicide bombers. But I don't want to resist all my life."

He argues that a non-violent strategy brings fewer Palestinian casualties. "I have no problem dying to get back my land, but I'd say to hell with my land if it just brought back our martyr who died last week. The life of a human being is more important than the land itself."

Often the most sensitive issue for the villagers has not been whether to take up arms, but whether to accept in their midst so many foreigners, and in particular so many Israeli demonstrators. Ahmad al-Khatib said it was the "most disputed question" and that many feared the Israelis were spying on them until they saw they, too, were being injured and arrested.

One of the first Israelis to join the Bil'in protest in its earliest days was Jonathan Pollack, 27, an activist and member of Anarchists Against the Wall who lives in Jaffa, just south of Tel Aviv. Although they warmly welcome him now, it was tense at first. "I'm still not one of their own and I don't pretend to be," he said.

Unlike most other joint peace initiatives, in this case the Israelis are in the minority and in the background. "I think it is very important that the struggle is Palestinian-led and that the colonial power relations are knowingly reversed," said Pollack.