By Josh Smith and Ju-min Park

SEOUL (Reuters) -South Korean President Yoon Suk Yeol said on Tuesday a new nuclear consultative group between South Korea and the United States would be a "starting point" to build a strong and effective deterrence against North Korea.

Officials from the United States and South Korea are meeting on Tuesday in Seoul for the first Nuclear Consultative Group discussion, aimed at better coordinating allied nuclear response in the event of a war with North Korea.

"Through a South Korea-U.S. alliance upgraded to a new nuclear-based paradigm, we will make substantial efforts to fundamentally block North Korea's nuclear and missile threats," Yoon told a briefing.

The NCG was first announced during the bilateral summit in Washington in April amid growing calls in South Korea for its own nuclear weapons, a step Washington opposes.

China and North Korea have criticised the group's formation as further raising tensions on the Korean peninsula.

On Monday North Korea, which test fired an intercontinental ballistic missile (ICBM) last week, condemned the NCG for "openly discussing the use of nukes" and warned against allied plans to increase displays of military force, including so-called "strategic assets" such as U.S. aircraft carriers, bomber aircraft, and submarines.

When asked whether South Korea will have a role in U.S. nuclear war planning, a senior U.S. administration official told Reuters the group was more about sharing information.

"A lot of the objective here is to make sure that our South Korean allies have more transparency, more access, more direct connection with planning, so that they can understand how government officials have long been thinking about what goes into defence and deterrence for South Korea," the official said, speaking on condition of anonymity to discuss the talks.

The inaugural meeting will be co-chaired by South Korea's Principal Deputy National Security Adviser Kim Tae-hyo and U.S. National Security Council Coordinator for Indo-Pacific Affairs Kurt Campbell.

"We will discuss information sharing, consultation system, steps for joint planning and implementation to strengthen nuclear deterrence against North Korea," Yoon's spokesperson, Lee Do-woon, told reporters on Monday.

U.S. Brigadier General John Weidner, who will represent U.S. Forces Korea at the talks, told a defence forum in Seoul last week he expected the discussions to establish a framework for new, bilateral table-top military exercises that will strengthen planning between the allies.

(Reporting by Ju-min Park and Josh Smith; Additional reporting by Steve Holland and David Brunnstrom in Washington and Soo-hyang Choi in Seoul; Editing by Ed Davies, Stephen Coates and Lincoln Feast.)