The tensions in Ukraine has started to flare up once again after NATO declined Russian demands about limiting NATO’s further expansion into eastern Europe. Russian troops have begun to pile up on the Ukrainian border, causing fears of a full-scale invasion of Ukraine.

Earlier on Wednesday, the U.S. has also sent a formal letter to the Russian government rejecting its demands about NATO and Ukraine. U.S. Ambassador to Russia John Sullivan delivered the U.S. document to the Russian Foreign Ministry.

Regarding the document, Blinken said, “We make clear that there are core principles that we are committed to uphold and defend – including Ukraine’s sovereignty and territorial integrity and the right of states to choose their own security arrangements and alliances,” he added “From our perspective, I can’t be more clear: NATO’s door is open, remains open, and that is our commitment.”

The European Union and the United States have also begun large-scale weapon shipments to Ukraine to pre-emptively prepare in the case of a Russian invasion. Javelin missiles, anti-armour, anti-tank and further ammunition and equipment are set to arrive in Kyiv, the capital of Ukraine.

Although the U.S and European Union have ruled out direct military confrontation, Blinken still stated that the U.S has “laid out a diplomatic path. We’ve lined up steep consequences should Russia choose further aggression. We’ve stepped forward with more support for Ukraine’s security and economy. And we and our partners and allies are united across the board,” he added, “It remains up to Russia to decide how to respond. We’re ready either way.”