LOS ANGELES, Jan. 1 (Xinhua) -- U.S. Customs and Border Protection (CBP) agents shoot tear gas Tuesday to deter about 150 migrants attempting to breach the U.S.-Mexico border fence into California.

The local NBC 7 news channel reported that roughly 150 migrants who attempted to climb over or crawl under the U.S.-Mexico border fence into California clashed with CBP agents early New Year's Day shortly after a group of 45 migrants were discovered by the agents.

The migrants threw rocks over the fence at CBP officers while the latter fought back with smoke, pepper spray and tear gas, the report said.

However, a volunteer group based in San Diego, a Southern California city along the border, told Xinhua that rubber bullets were used by CBP agents in the clash.

These migrants were "attacked by gas and rubber bullets," said Enrique Morones, founder of Border Angels, adding that "rock throwing is not endorsed" by his non-profit organization which advocates human rights, humane immigration reform and social justice.

The San Diego City News Service cited CBP officials' words as reporting that the tear gas was fired because some migrants on the Mexican side threw rock at agents to prevent them from helping children, who were being passed over the concertina wire.

"No agents witnessed any of the migrants at the fence line, including children, experiencing effects of the chemical agents, which were targeted at the rock throwers further away," CBP said.

Reports said several teenagers were put over the fence's barbed wire in heavy jackets and blankets and 25 migrants, including two teenagers, were detained.

Morones said he felt outraged after a similar violent incident happened again.

"Last month two children died in border patrol custody, last month they fired tear gas at women and children and several were injured. Last night they did it again," he told Xinhua.