China and Russia have reportedly blocked a U.S. bid to impose additional UN sanctions on North Korea.

According to Reuters and AFP, China and Russia delayed a U.S. bid to slap UN sanctions on five North Koreans who are allegedly responsible for the North's missile development.

Last week, the U.S. imposed unilateral sanctions on six North Koreans, one Russian and a Russian firm after a series of missile launches by the North. 

U.S. Ambassador to the UN Linda Thomas-Greenfield proposed five of them also be subjected to a UN travel ban and asset freeze. 

The proposal required agreement by consensus by the Security Council's five permanent members and ten non-permanent members.  

China, however, is said to have placed a "hold" on the U.S. proposal on Thursday, saying that it needed more time to study the sanctions proposal. According to diplomats, Russia also made a similar move.

The move by China and Russia reportedly came ahead of a closed-door UN Security Council meeting on North Korea on Thursday.

According to AFP, the block lasts for six months under current UN rules. After that, another council member can extend the block for three more months before the proposal is permanently removed from the negotiating table.