Germany's president on Sunday said the country should not "block" the United States from sending cluster bombs to Ukraine, while defending its opposition to the use of the controversial weapon.

"Germany's position against the use of cluster munitions is as justified as ever. But we cannot, in the current situation, block the United States," said President Frank-Walter Steinmeier in an interview with German broadcaster ZDF.

If Ukraine no longer has the means to defend itself or if those supporting the war-stricken country back down, "it would be the end of Ukraine", said the president, whose powers are largely ceremonial.

The United States announced Friday new military aid to support the Ukrainian army to counter the Russian invasion, which include cluster munitions, crossing a new threshold in the type of weaponry supplied to Kyiv.

Washington's announcement drew strong criticism from NGOs and embarrassed several European countries.

The highly controversial weapons can disperse up to several hundred small explosive charges, which risk causing many civilian casualties.

They are banned by numerous countries, notably in Europe, who are signatories to a 2008 Oslo Convention, to which neither the United States nor Ukraine are parties.

Steinmeier recalled having signed the convention on behalf of his country while he was foreign affairs minister, while adding Germany must continue to "stand by the victims" in this war.

On Friday, a German government spokesman said that they believed the US decision to send cluster munitions would not have been made lightly, and pointed out that Russia has already used such weapons on Ukrainian territory.

France and the United Kingdom have expressed their opposition to the use of the weapon, but also shared their understanding of the United States' decision in its decision to help Ukraine.