"I believe that membership will bring tensions again," he said, citing the high probability of an immediate conflict with Russia if Ukraine joins NATO.
At the same time, Bettel expressed his support for Kyiv's aspirations of joining the EU.
A Ukrainian delegation also present at the meeting made it clear that it sees NATO membership as the only real security guarantee in the event of a ceasefire with Russia.
Ukraine "will not accept any alternatives, imitations or substitutes for full NATO membership," the country's Foreign Ministry said in a statement released before the meeting.
NATO membership requires the unilateral approval of all 32 member states of the organization.
On the same day, NATO Secretary General Mark Rutte said that additional military aid to Kyiv would be the focus of the meeting in Brussels, rather than Ukraine's membership in the alliance.
In recent days, Ukrainian President Volodymyr Zelenskyy have articulated a shift in Kyiv's approach to ending the war through negotiations. The president suggested that Ukraine could accept a temporary loss of some of its territory if it came with NATO membership. To avoid immediately triggering an armed conflict with Russia when Ukraine joins the alliance, the Article 5 clause could be tailored to apply only to Ukrainian regions under government control.