Massive tear gas clouds fill air as Turkish police move toward Gezi Park

 ISTANBUL (CNN) -- Riot police fired massive clouds of tear gas across Taksim Square in Istanbul on Tuesday and used water cannons, sending protesters running.

Thick smoke blanketed the area -- some of it in Gezi Park, the central point of the protests.

The government had promised to allow protesters to remain in Gezi Park as long as they were peaceful. But CNN's Arwa Damon, inside the park, saw police shoot tear gas canisters in.

Protesters responded with fireworks -- a sign of defiance.

Authorities lined up close to the park, then moved in line to an area nearby.

"There's a spirit of determination" and "solidarity" in the park, Damon said.

Throughout the day, protesters have called on each other to try to keep things calm -- and to keep protests peaceful.

When the fog of heavy tear gas lifted in Taksim Square, the area in which tens of thousands of people had been gathered -- and had been throwing rocks at riot police -- was empty of protesters.

But soon, thousands of protesters started to work their way back in.

The assault on the area marked a return to the more heavy-handed tactics Turkish authorities used in the earlier days of the protests.

The protests at first had focused on the environment -- opposition to a plan to build a mall at the park -- but quickly grew into a battle against what demonstrators call the government's increasingly authoritarian tactics.

Earlier Tuesday, police and protesters battled over a new barrier inside the square.

Protesters lobbed Molotov cocktails at armored vehicles and burned one. Police responded by spraying water cannons.

In a game of cat-and-mouse, the demonstrators, using wooden boards as shields, would pull back -- only to return, lobbing cocktails and firecrackers and flashing "victory" signs.

For more coverage, go to CNN.