The Russian president, Vladimir Putin, has warned that the escalating North Korean crisis could cause a “planetary catastrophe” and huge loss of life.

“Ramping up military hysteria in such conditions is senseless; it’s a dead end,” he told reporters in China. “It could lead to a global, planetary catastrophe and a huge loss of human life. There is no other way to solve the North Korean nuclear issue, save that of peaceful dialogue.”

On Sunday, North Korea carried out its sixth and by far its most powerful nuclear test to date. The underground blast triggered a magnitude-6.3 earthquake and was more powerful than the bombs dropped by the US on Hiroshima and Nagasaki during the second world war.

Putin was attending the Brics summit, bringing together the leaders of Brazil, Russia, India, China and South Africa. Speaking on the final day of the summit in Xiamen, China, he said Russia condemned North Korea’s provocations but said further sanctions would be useless and ineffective.

Foreign interventions in Iraq and Libya had convinced the North Korean leader, Kim Jong-un, that he needed nuclear weapons to survive, Putin said.

“We all remember what happened with Iraq and Saddam Hussein. His children were killed, I think his grandson was shot, the whole country was destroyed and Saddam Hussein was hanged … We all know how this happened and people in North Korea remember well what happened in Iraq.

“They will eat grass but will not stop their [nuclear] programme as long as they do not feel safe.”

Putin’s warning came as South Korea refused to rule out redeploying US tactical nuclear weapons on its territory – a move that could seriously harm efforts to ease tensions as signs emerged that Pyongyang was preparing to launch another intercontinental ballistic missile (ICBM).

Seoul has routinely dismissed the option of basing US nuclear weapons on South Korean soil for the first time since the 1990s, but the country’s defence minister, Song Young-moo, said “all available military options” were being considered to address the growing threat from North Korean missiles.

On Tuesday, South Korean warships conducted live-fire drills, with further exercises planned this week. “If the enemy launches a provocation above water or under water, we will immediately hit back to bury them at sea,” said Capt Choi Young-chan, commander of the 13th Maritime Battle Group.

The drills came hours after Donald Trump and his South Korean counterpart, Moon Jae-in, agreed to remove restrictions on the size of Seoul’s missile warheads and approved a deal to sell it “many billions of dollars’” worth of US military weapons and equipment.

Song raised the possibility of redeploying US nuclear weapons after the North’s nuclear test in remarks to the South’s national assembly, according to the Yonhap news agency.

His remarks were later clarified, with spokesman Moon Sang-gyun saying there was “no change” in Seoul’s principle of working towards the complete denuclearisation of the peninsula.

Moon said Song had simply been stressing the need to “review all available options from the military perspective, and find a realistic way forwards”.

Kim Hyun-wook, a professor at the Korea National Diplomatic Academy in Seoul, said: “No one in South Korea is seriously proposing that the US reintroduce strategic assets [such as nuclear weapons]. That’s something they might discuss further down the line, but there are no plans for that to happen right now.”

Calls have also been growing in South Korea for the country to develop a nuclear deterrentindependent of the US.

Song’s comments came amid reports that North Korea may be preparing to launch another ICBM from a site on its west coast.

North Korea has been observed moving what appeared to be a long-range missile towards its west coast, according to South Korea’s Asia Business Daily. The newspaper claimed the missile had been transported towards the launch site overnight on Monday to avoid surveillance.

South Korea’s defence ministry said it was unable to confirm the report, although ministry officials told parliament on Monday the Pyongyang regime was preparing to launch more missiles.

In the past, North Korea has displayed its military capability to coincide with significant national anniversaries. That is fuelling speculation that an ICBM launch could come as early as this Saturday, when the country marks the 69th anniversary of its founding. The regime’s fifth nuclear test came on the same date, 9 September, last year.

Washington appears to have moved to ease South Korean doubts about US commitment to its security after Trump openly accused its east Asian ally of “appeasing” Pyongyang by holding out for a negotiated solution to its nuclear and ballistic missile programmes.

The agreement from the US to remove warhead restrictions on South Korean missiles will allow Seoul to develop more powerful weapons that would increase its pre-emptive strike capabilities against the North.

Trump’s appeasement comment, together with his reported threat to take the US out of a free trade agreement with South Korea, have triggered calls for Seoul to win stronger security assurances from Washington.

In an editorial published on Tuesday, the Korea Herald said: “The Seoul government’s most urgent job is to secure – based on a tight alliance with the US – defence and deterrence capability against possible nuclear and missile attacks from the North.”

The newspaper called for the quick deployment of the last four of six terminal high altitude area defence (Thaad) systems, but said that was only a first step.

The diplomatic focus is expected to shift to the UN security council later on Tuesday, with a vote expected on a resolution condemning the North’s latest nuclear test.

One drastic measure reportedly under consideration by US officials – a ban oil exports to North Korea – is likely to be opposed by Russia and China.

Beijing supplies roughly 500,000 tonnes of crude oil to North Korea every year as well as 200,000 tonnes of oil products, according to South Korean and UN data.

China opposes any measure that could cause instability and topple the regime of Kim Jong-un, sparking a refugee crisis and potentially allowing tens of thousands of South Korean and US troops to move north as far as the Chinese border.

On Monday, the US ambassador to the UN, Nikki Haley, accused North Korea of “begging for war”, adding that the time had come for the security council to impose “the strongest possible” sanctions after Sunday’s test of what Pyongyang claimed was a hydrogen bomb that could be loaded on to an ICBM.