BEIJING, March 20 (Xinhua) -- Property rights are the cornerstone of a socialist market economy, and protecting these rights has always been an important element of the government's agenda, Premier Li Keqiang said Tuesday.

"Private investment has been weak for some time due to problems in property rights protection and some other factors," Li said at a press conference after the conclusion of the annual session of the top legislature. "We have paid high attention to this problem."

He stressed that private businesses now account for about half of government tax revenue, and contribute 90 percent to newly-added urban employment.

"A contract must be honored and no legitimate contract should be treated as a piece of scrap paper," Li said, adding that the government would reassure all property owners about the protection of their property rights.