Russia test-fired missiles over distances of thousands of miles on Tuesday to simulate a "massive" nuclear response to an enemy first strike, Reuters reported.

"Given the growing geopolitical tensions and the emergence of new external threats and risks, it is important to have modern and constantly ready-to-use strategic forces," President Vladimir Putin said as he announced the exercise.

It took place at a critical moment in the Russia-Ukraine war, after weeks of Russian signals to the West that Moscow will respond if the United States and its allies allow Kyiv to fire longer-range missiles deep into Russia.

On Monday NATO said that North Korea has sent troops to western Russia, something Moscow has not denied.

In televised comments, Defence Minister Andrei Belousov told Putin that the purpose of the drill was to practice delivering "a massive nuclear strike by strategic offensive forces in response to a nuclear strike by the enemy".

The exercise involved Russia's full nuclear "triad" of ground-, sea- and air-launched missiles.

A Yars intercontinental ballistic missile was launched from Plesetsk cosmodrome in northwest Russia to Kamchatka, a peninsula in the far east.

Sineva and Bulava ballistic missiles were fired from submarines, and cruise missiles were launched from strategic bomber planes, the defence ministry said.

The 2-1/2-year-old war is entering what Russian officials say is its most dangerous phase as the West considers how to shore up Ukraine while Russian forces advance in the east of the country.

Putin said using nuclear weapons would be an "extremely exceptional measure".

"I stress that we are not going to get involved in a new arms race, but we will maintain nuclear forces at the level of necessary sufficiency," he said.

He added that Russia was moving to new "stationary and mobile-based missile systems" which have a reduced launch preparation time and could overcome missile defence systems.

The drill follows an Oct. 18 exercise in the Tver region, northwest of Moscow, involving field movements by a unit equipped with Yars intercontinental ballistic missiles, capable of striking U.S. cities, Reuters reported.

Nuclear Signals

Since the start of the war, Putin has sent a series of pointed signals to the West, including by changing Russia's position on major nuclear treaties and announcing the deployment of tactical nuclear missiles to neighbouring Belarus.

Ukraine has accused him of nuclear blackmail. NATO says it will not be intimidated by Russian threats.

Last month the Kremlin leader approved changes to the official nuclear doctrine, extending the list of scenarios under which Moscow would consider using such weapons.

Under the changes, Russia would consider any assault on it supported by a nuclear power to be a joint attack - a warning to the United States not to help Ukraine strike deep into Russia with conventional weapons.

Putin has said that Russia does not need to resort to the use of nuclear weapons in order to achieve victory in Ukraine.

Russia is the world's largest nuclear power. Together, Russia and the U.S. control 88% of the world's nuclear warheads.

U.S. officials say they have seen no change to Russia's nuclear deployment posture during the war.

But the United States in 2022 was so concerned about the possible use of tactical nuclear weapons by Russia that it warned Putin over the consequences of using such weapons, according to Central Intelligence Agency Director Bill Burns.

North Korea's foreign minister, Choe Son Hui, is on her way to Moscow, state media KCNA and Russian officials said on Tuesday, for her second trip to Russia in six weeks amid rising concerns about Pyongyang's involvement in Moscow's war in Ukraine, Reuters reported.

KCNA said a delegation led by Choe left on Monday for an official visit to Russia, without elaborating.

Russia's ambassador to Pyongyang, Alexander Matsegora, saw off Choe at the airport, the Russian embassy said in a statement posted on the embassy's Vkontakte social media page.

"The visit of the head of the DPRK Foreign Ministry to the Russian Federation is taking place within the framework of a strategic dialogue - following an agreement to enhance ties reached by the leaders of our countries during the June 2024 summit," the statement said.

DPRK stands for North Korea's official name, the Democratic People's Republic of Korea.

During a televised cabinet meeting, South Korean President Yoon Suk Yeol said "illegal" military cooperation between Russia and North Korea posed a serious threat to the international community, read the report.

"I want everyone to be on alert about risk management," Yoon told the meeting.

Choe's visit comes as NATO joined Seoul, Washington and Kyiv in confirming Pyongyang's dispatch of troops to Russia, saying that North Korean military units had been deployed to Russia's Kursk region on the border with Ukraine.

The Pentagon said on Monday that Washington would not impose new limits on Kyiv's use of American weapons if North Korea entered Moscow's war against Kyiv. It also said that North Korea had sent 10,000 troops to eastern Russia for training, up from its estimate of 3,000 on Wednesday.

U.S. President Joe Biden called the situation "very dangerous".

NATO Secretary-General Mark Rutte, after a meeting on Monday with a South Korean delegation, said the deepening military ties between Moscow and Pyongyang posed a threat to both Indo-Pacific and Euro-Atlantic security, Reuters reported.

South Korea's president, in a phone call with European Commission President Ursula von der Leyen, said the deployment of North Korean troops to the front lines of the war in Ukraine may come sooner than expected.

Since the meeting of North Korean leader Kim Jong Un and President Vladimir Putin in Russia's Far East last year, North Korea and Russia have upgraded their military ties. They met again in June this year to sign a comprehensive strategic partnership that includes a mutual defence pact.

Egypt has proposed an initial two-day ceasefire in Gaza to exchange four Israeli hostages of Hamas for some Palestinian prisoners, Egypt's president said on Sunday as Israeli military strikes killed 45 Palestinians across the enclave.

Egyptian leader Abdel Fattah al-Sisi made the announcement as efforts to defuse the devastating, more than year-long war resumed in Qatar with the directors of the CIA and Israel's Mossad intelligence agency taking part, Reuters reported.

Speaking alongside Algerian President Abdelmadjid Tebboune during a press conference in Cairo, Sisi also said that talks should resume within 10 days of implementing the temporary ceasefire in efforts to reach a permanent one.

There was no immediate comment from Israel or Hamas but a Palestinian official close to the mediation effort told Reuters: "I expect Hamas would listen to the new offers, but it remains determined that any agreement must end the war and get Israeli forces out of Gaza."

Israel has said the war cannot end until Hamas has been wiped out as a military force and governing entity in Gaza.

The U.S., Qatar and Egypt have been spearheading negotiations to end the war that erupted after Hamas fighters stormed into southern Israel on Oct. 7 last year, killing 1,200 people and taking more than 250 hostages, by Israeli tallies.

The death toll from Israel's retaliatory air and ground onslaught in Gaza is approaching 43,000, Gaza health officials say, with the densely populated enclave in ruins.

An official briefed on the talks told Reuters earlier on Sunday that negotiations in Doha will seek a short-term ceasefire and the release of some hostages being held by Hamas in exchange for Israel's release of Palestinian prisoners.

The objective, still elusive after multiple mediation attempts, is to get Israel and Hamas to agree to a halt in fighting for less than a month in the hope this would lead to a more permanent ceasefire.

At least 43 of those killed in Gaza on Sunday were in the north of the enclave, where Israeli troops have returned to root out Hamas fighters who it says have regrouped there.