SEOUL, Mar. 29 (Reuters) - Russia's move to effectively disband the panel of experts monitoring longstanding United Nations sanctions against North Korea points to a "grim future" for the sanctions enforcement, three former members of the panel told Reuters.

Russia vetoed the annual renewal of the multinational panel of experts on Thursday, which has spent the last 15 years monitoring U.N. sanctions against North Korea over its nuclear weapons and ballistic missile programs.

China, North Korea's only military ally and its largest trading partner, abstained. Beijing and Moscow have denied breaking sanctions but have blocked new measures at the UN Security Council and advocated lifting some existing sanctions on North Korea, blaming the West and its allies for exacerbating tensions.

Diplomats said it appeared unlikely there would be another vote to try to renew the mandate before it expires on April 30.

The veto highlights a rare diplomatic dividend for Pyongyang and underlines its deepening ties with Moscow, which have included unprecedented shipments of ballistic missiles and ammunition for use in the war in Ukraine as well as possible fuel supplies for North Korea, according to U.S. and South Korean officials and independent analysts.

Both Moscow and Pyongyang have denied arms deals, but have vowed to deepen military relations and Russia’s spy chief visited North Korea this week to vow a united front against “attempts to increase pressure from external forces.”

The vote was significant and represents a major turning point in the international sanctions regime against North Korea, said Aaron Arnold, a former member of the panel who now works as a sanctions expert at Britain's Royal United Services Institute (RUSI).

“Russia’s vote, along with its blatant violation of sanctions by buying conventional arms from North Korea, years long history of ignoring their obligations, and at least tacit support from China suggest that the future is grim for the DPRK sanctions regime,” he said, using the initials of North Korea's official name, the Democratic People's Republic of Korea.