Soldiers have fired on Palestinian protesters in Lebanon, killing at least three people and injuring about 40, witnesses and medics say.
The protest began at the Baddawi refugee camp
The Palestinians were trying to break through a checkpoint to get back to their homes in the Nahr al-Bared refugee camp in northern Lebanon.
The camp has been the scene of weeks of clashes between the army and Islamists.
Fighting at the camp and associated unrest has left 200 people dead since 20 May.
This makes it Lebanon's worst internal violence since the 1975-90 civil war.
Witnesses said soldiers fired in the air above the heads of at least 100 demonstrators.
When the crowd did not disperse, the troops fired automatic rifles at the protesters.
One witness said the demonstrators did not provoke the soldiers.
The army issued a statement saying its troops had to respond after the protesters blocked the main road with burning tyres and attacked soldiers with sticks and sharp objects.
An unnamed army spokesman was earlier quoted by the AFP as saying that soldiers only fired warning shots.
It is the first time since the fighting started that trouble has erupted between the Lebanese army and the Palestinian refugees, the BBC's Kim Ghattas in Beirut says.
Weeks of clashes between the army and Fatah al-Islam militants at the camp have also caused tensions between Palestinians and Lebanese, our correspondent says.
Human Rights Watch issued a statement, deploring the fact that the army did not have the necessary non-lethal means to disperse the crowd.
It also called for an independent investigation into the incident.
Some 20,000 Palestinian refugees had fled the Nahr al-Bared camp since the fighting began.
Most of them have been sheltered since then in the overcrowded Baddawi camp, about 5km (three miles) away from Nahr al-Bared.
Although the stand-off between the army and the militants is continuing, the refugees have been demanding to be allowed to return home.
Lebanon has 12 refugee camps housing more than 350,000 Palestinians. They are people who fled or were forced to leave their homes when Israel was created in 1948, or their descendants.