Ukraine says it urgently needs more weapons from its Western allies to defend itself against Russia.
Foreign Minister Dmytro Kuleba told a Nato meeting that more atrocities against civilians could happen if Ukraine doesn't get more military aid.
Nato chief Jens Stoltenberg said members of the alliance had agreed more support for Ukraine.
Russia has warned that "pumping weapons into Ukraine" will have a "negative effect" on peace talks.
Mr Kuleba said he was looking for "weapons, weapons and weapons", but he added that Ukraine was offering Nato a "fair deal".
"You provide us with everything that we need, and we will fight for our security but also for your security, so that President Putin will have no chance to test Article 5 of the North Atlantic Treaty," he said.
Article 5 is the key part of the Nato treaty that says that an attack on one Nato country is considered an attack on all.
"Either you help us now - and I'm speaking about days, not weeks, or your help will come too late, and many people will die, many civilians will lose their homes, many villages will be destroyed," Mr Kuleba said.
Ukraine is not a part of Nato but has been receiving military aid from its members.
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Mr Stoltenberg said members of the alliance were prepared to increase support.
"After the invasion, allies stepped up with additional military support, with more military equipment, and it was a clear message from the meeting today that allies should do more and are ready to do more to provide more equipment, and they realise and recognise the urgency," he said.
"We are closely coordinating and discussing these issues with Ukraine, so allies are providing and are willing to do more when it comes to military support."
Over 30 countries including the UK have provided military aid to Ukraine, including €1bn (£800m) from the EU and $1.7bn (£1.3bn) from the US.
So far Western supplies have been limited to arms, ammunition, and defensive equipment like anti-tank and anti-aircraft missile systems.
Nato members fear that supplying Ukraine with heavier offensive equipment like tanks and fighter jets could lead to direct open conflict between Russia and the alliance.
Russia warned on Thursday that the supply of weapons to Ukraine is harming any prospect of ending the war.
"Pumping weapons into Ukraine will not contribute to the success of Russian-Ukrainian talks," Kremlin spokesperson Dmitry Peskov said, referring to the peace negotiations between the two countries.
Speaking at Nato's headquarters ahead of Thursday's meeting, UK Foreign Secretary Liz Truss said "in the face of Putin's appalling aggression...we are stepping up our supply of weapons to Ukraine."
Ms Truss is yet to detail what those supplies will include, but the Times newspaper has reported that the UK is preparing to supply Kyiv with armoured vehicles.
It comes after reports this week that the Czech Republic is sending Soviet-era tanks to help Ukrainian forces, which if confirmed would make it the first Nato country to do so.
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