This past week has seen the most significant escalation in hostilities that Ukraine has witnessed since Russia's full-scale invasion and marks a new chapter in the nearly three-year war — one tinged with uncertainty and fear.

It began with U.S. President Joe Biden reversing a longstanding policy by granting Kyiv permission to deploy American longer-range missiles inside Russian territory and ended with Moscow striking Ukraine with a new experimental ballistic weapon that has alarmed the international community and heightened fears of further escalation.

Here is a look at the events in Ukraine in the span of a week that has fundamentally altered the stakes of the war:

SUNDAY: U.S. approves strikes using longer-range American weapons

Washington eased limits on what Ukraine can strike with its American-made Army Tactical Missile System, or ATACMS, after months of ruling out such a move over fears of escalating the conflict and bringing about a direct confrontation between Russia and NATO.

The change came after the U.S., South Korea and NATO said North Korean troops were inside Russia and being deployed to help Moscow drive Ukrainian troops from Russia’s Kursk region. But the scope of the new firing guidelines wasn’t clear.

MONDAY: Russia warns of escalation if Western weapons are used inside its territories

The Kremlin warned that Biden’s decision would escalate international tensions even higher.

“It is obvious that the outgoing administration in Washington intends to take steps, and they have been talking about this, to continue adding fuel to the fire and provoking further escalation of tensions around this conflict,” spokesman Dmitry Peskov said.

TUESDAY: Ukraine fires American longer-range missiles into Russia for first time; Putin lowers threshold for nuclear attack

Ukraine fired several ATACMS, striking an ammunition warehouse in Russia’s Bryansk region, the first time Kyiv had used the weapons inside enemy territory, according to widespread reports. Ukrainian officials have not officially confirmed the strikes which occurred on the 1,000th day since the invasion.

Also Tuesday, Russian President Vladimir Putin formally lowered the threshold for using nuclear weapons, opening the door to a potential nuclear response by Moscow to even a conventional attack by any nation supported by a nuclear power. That could include Ukrainian attacks backed by the U.S.

WEDNESDAY: U.S. approves giving Ukraine anti-personnel mines

In the second major shift in U.S. policy, the Biden administration announced it will give Ukraine antipersonnel mines to help slow Russia’s battlefield advances. Biden had previously put off signing off on this because of international objections to the use of such mines due to the risks they pose to civilians. Russia deploys them freely.

U.S. Defense Secretary Lloyd Austin said the shift in Washington’s policy was needed to counter changing Russian tactics.

Ukraine also struck targets inside Russia using the British Storm Shadow missile, an equivalent of the ATACMS system, further vexing Moscow.

The U.S. and some other Western embassies in Kyiv temporarily closed in response to the threat of a potentially major Russian aerial attack on the Ukrainian capital.

THURSDAY: Russia uses new, experimental ballistic missile for the first time

The Kremlin fired a new intermediate-range ballistic missile at Ukraine in response to Kyiv’s use of American and British missiles, Putin said.

In a televised address to the country, the Russian president warned that U.S. air defense systems would be powerless to stop the new missile, which he said flies at 10 times the speed of sound and which he called the Oreshnik — Russian for hazelnut tree — based on Russia’s RS-26 Rubezh intercontinental ballistic missile, which can carry nuclear warheads.

Putin also said it could be used to attack any Ukrainian ally whose missiles are used to attack Russia. Moscow gave Washington a 30-minute warning of the attack, which struck a weapons factory in the central Ukrainian city of Dnipro.

FRIDAY: NATO calls emergency meeting as Ukraine's parliament closes

NATO and Ukraine scheduled emergency talks slated for Tuesday, the alliance said. The meeting will be held at the request of Ukraine and will convene at the level of ambassadors.

Ukraine’s parliament also canceled a session as security was tightened in the city. Lawmakers said there was a credible threat of an attack on government buildings.

Ukraine's partners weighed in on the dangerous new phase of the conflict. Poland’s Prime Minister Donald Tusk said the conflict is “entering a decisive phase" and “taking on very dramatic dimensions.”

SATURDAY: Zelenskyy says he believes war could be ended next year

Ukrainian President Volodymyr Zelenskyy said Saturday he was confident the war could be ended in 2025.

“There are appropriate steps for this, they are included in our peace formula," he told journalists attending the Grain from Ukraine international conference on food security in Kyiv. "We realize that Russia will not take all these steps. But there is a U.N. charter and we hope that all our steps based on the U.N. charter will be supported by our partners.”

“We are open, I will say it again, and by the way, to the leaders of African countries, Asia, and the Arab states ... we are ready to see their proposals," he said. "I also want to see the proposals of the new president of the United States of America. I think we will see these proposals in January. And I think we will have a plan to end this war.”