By Hyunsu Yim

SEOUL, Oct 17 (Reuters) - South Korea, the United States and Japan have completed work on a three-way communication hotline, Yonhap news agency reported on Tuesday citing a senior Seoul official, in a further sign of growing trilateral security cooperation.

The hotline comes at a time of military tensions with North Korea and China's growing regional influence. The three countries' leaders announced a commitment to consult each other in times of crisis at a summit in Camp David in August.

Technical tests of the system have been completed, Yonhap said, citing the anonymous source. The hotline is to be used by the leaders or their top national security advisers in times of security crises, it said.

South Korea's foreign ministry did not immediately confirm the report.

Nuclear envoys from the three countries are holding two days of talks from Monday in Jakarta to discuss heightened tensions stemming from North Korea's nuclear program and closer military cooperation between Pyongyang and Moscow.

The meeting comes amid a new accusation by the United States that the North recently provided Russia with a large shipment of weapons, which it said was an indication of expanded military relationship between the two countries.

North Korean leader Kim Jong Un's made a rare trip to Russia to meet President Vladimir Putin last month, fanning concerns they could shore up Russia's military in Ukraine while North Korea obtains missile technology banned under U.N. resolutions.

Russia's foreign minister, Sergei Lavrov, will visit North Korea this week, according to North Korea's state media KCNA and Russia's foreign ministry.

On Tuesday, South Korean President Yoon Suk Yeol pledged to boost the defence industry as a key part of national security strategy, addressing the opening of the country's largest-ever defence exhibition.

"Overwhelming" capabilities of the South Korea-U.S. alliance are on display at the event, Yoon said at the biennial Seoul International Aerospace and Defense Exhibition $(ADEX)$, noting U.S. military hardware including a rare flyover by a U.S. nuclear-capable B-52 strategic bomber.

Pyongyang has repeatedly criticised the United States over the deployment of strategic assets in the region, including the recent arrival of a U.S. aircraft carrier, calling it a provocation.

(Reporting by Hyunsu Yim. Editing by Gerry Doyle)

((Hyunsu.Yim@thomsonreuters.com;))