Boeing plans to cut hundreds of additional jobs in its civil aviation business due to slowing sales, a spokesman said Monday.

"In an ongoing effort to increase overall competitiveness and invest in our future, we are reducing costs and matching employment levels to business and market requirements," Boeing spokesman Doug Alder said.

The downsizing will come through a mix of "attrition, leaving open positions unfilled, a voluntary layoff program and in some cases, involuntary layoffs," he added.

The cuts will take effect June 23, and primarily affect production sites in the state of Washington, a person familiar with the situation said. Boeing is the biggest private employer in the Northwest US state, with more than 70,000 workers.

At the start of the year, Boeing eliminated 305 engineering jobs and cut 1,500 mechanics as part of a voluntary programs.

Boeing plans additional job cuts later this year, a person close to the matter said. Boeing currently has 146,962 employees, down 7.6 percent from the year-ago level.

Shares rose 1.7 percent to $178.65 in afternoon trading.