Pro-Palestinian protesters occupy Columbia University building

Pro-Palestinian activists occupied a building at Columbia University early on Tuesday, escalating a battle with administrators who have begun suspending students for refusing to dismantle tents set up on the New York campus.

Protesters entered Hamilton Hall - the site of student protests dating back to the 1960s - and suspended a banner reading "Hind's Hall" from an upper floor. Others outside blocked the doors with outdoor tables and linked arms to form a barricade in front.

"This building is liberated in honor of Hind, a six-year-old Palestinian child murdered in Gaza by the Israeli occupation forces funded by Columbia University," a protester shouted from inside, with those outside repeating each phrase.

Israel has denied targeting civilians in its war on Hamas in Gaza, accusing the militants of hiding among them.

Minutes after the protesters gained access to the building, New York City police officers arrived outside the school gates in unmarked cars, the Columbia Spectator newspaper reported. It said police told the paper they would only enter school grounds if someone was injured.