EU states decided to provide Ukraine with the shells until March 2024 to support the country in its defence against Russia, but only about 300,000 shells have been delivered so far.
Fulfilling the pledge was a “challenge,” Michel said.
“We are working to get 1 million rounds of artillery ammunition to Ukraine,” he said.
“It will take slightly more time than we hoped, but it will happen,” he added.
Earlier this month, German Defence Minister Boris Pistorius said that the bloc is likely to miss its target.
EU top diplomat Josep Borrell had however insisted that the European defence industry will have the capacity to produce the promised shells by next March.
New commitments from the EU for military aid for Kiev have been stalling in recent months, as the bloc is struggling to beef up arms production capacities.
Furthermore, plans to provide Ukraine with military support worth €20 billion ($21.9 billion) until 2027 are unlikely to be approved.
“We all know that we need to do more – more missiles, more ammunition, more air defence systems – and faster,” Michel said.
“This is an obligation, an obligation towards the Ukrainian people, but also towards our citizens. By protecting Ukraine, we protect ourselves,” he added.