Chinese police investigating an expired meat scandal have detained another official from a local unit of US food supplier OSI Group, bringing the total to six, the company said.

Police previously said they were holding five officials of Shanghai Husi Food Co., a subsidiary of OSI which operated a factory shut down by authorities for mixing out-of-date meat with fresh product and selling it to fast food chains in China. Its clients include McDonald's and KFC.

Neither OSI nor state media gave the identities of the detained officials, but the official Xinhua news agency said they were "senior executives".

"We can confirm that as part of the on-going governmental investigation into our company, the Shanghai branch of the Public Security Bureau has detained six employees of Shanghai Husi," OSI said in a statement provided to media on Monday.

"Throughout this investigatory process, we have been and will continue to provide our complete cooperation to all authorities involved," it said.

Besides the government investigation, OSI is conducting an internal probe after shaking up the management of its China operations, top company officials told a news conference in Shanghai last week.

Xinhua also reported late Monday that Shanghai's food safety and commerce agencies were investigating OSI's China headquarters, demanding documents and greater cooperation.

The OSI Shanghai factory's customers in China included McDonald's, KFC, Pizza Hut, coffee chain Starbucks, Burger King, 7-Eleven convenience stores and Papa John's Pizza, according to the companies.

McDonald's says it has already severed its relationship with OSI, which has caused the fast food giant to pull meat items -- including Big Macs and Chicken McNuggets -- from many of its more than 2,000 China outlets since last week.

The National Business Daily newspaper reported Monday that some McDonald's restaurants in Beijing had resumed selling chicken items and beef burgers following the widespread shortages.

McDonald's said Monday that the recent incident has caused a "significant negative impact" on sales in China, Japan and some other markets.

The scandal has spread to Japan and Hong Kong. McDonald's Japan had stopped selling products with chicken sourced from China and introduced nuggets made from tofu, though it denied a link to the meat scandal.

In Hong Kong -- a special administrative region of China -- McDonald's suspended sales of chicken nuggets and several other items.