Thousands of demonstrators took to the streets of Midtown Manhattan on Thursday in protest of Israel’s war in Gaza and its recent strikes on Lebanon, denouncing Prime Minister Benjamin Netanyahu of Israel, who had arrived in New York ahead of a scheduled Friday address to the U.N. General Assembly.

Several protests overlapped throughout the day, with the largest winding through Manhattan’s streets and stopping traffic. Tensions between police officers and protesters flared after dark on the Upper East Side, where roughly a dozen protesters were arrested over the course of several hours.

The demonstrations, organized by several pro-Palestinian groups including Within Our Lifetime and Jewish Voice for Peace, were peaceful and largely orderly for most of the day but escalated after one group of protesters made its way uptown from Grand Central Terminal.

Outside the Metropolitan Museum of Art, police officers on bicycles surrounded a defiant crowd on the sidewalk. On the museum steps, officers held their bicycles in front of them to block the crowd from the front of the building.

After the march moved on to Park Avenue, officers told the protesters to clear the road and began making arrests when they refused.