The UK government spokesman said that Britain will never accept a customs border between Northern Ireland and the rest of the UK.
"The prime minister has been clear that we will never accept a customs border between Northern Ireland and the rest of the United Kingdom. We are also committed to maintaining the integrity of our own internal market. That position will not change," the spokesman said.
"The Commission's proposals did not achieve this, which is why we have put forward our own backstop solutions for customs," he added.
All EU member states are part of the customs union, where all countries have a common tariff on goods transported from outside of the EU, while between the states within the bloc there are no tariffs.
The British government said it is leaving the bloc's customs union in order to be able to arrange its own trade deals with other countries around the world and now the UK has to agree on an option to replace it.