European Commission chief Jean-Claude Juncker warned Prime Minister Boris Johnson on Wednesday that there are "problematic points" in Britain's new proposed Brexit withdrawal deal.
Juncker highlighted concerns about London's proposed customs regime aimed at avoiding checks on the border between British-ruled Northern Ireland and EU member Ireland.
But he recognised "positive advances" in the British offer during a phone call with Johnson, telling him that EU negotiators would now "examine the legal text objectively".
The proposal is Britain's suggestion for how to do away with the so-called "Irish backstop", which Johnson's predecessor Theresa May agreed to but which the British parliament rejected.
"President Juncker welcomed Prime Minister Johnson's determination to advance the talks ahead of the October European Council and make progress towards a deal," Juncker's office said in a statement.
"He acknowledged the positive advances, notably with regards to the full regulatory alignment for all goods and the control of goods entering Northern Ireland from Great Britain."
"Another concern that needs to be addressed are the substantive customs rules."