Borrell said this was the way to interpret the report recently adopted by the Committee on Foreign Affairs which the European Parliament is due to vote on at a plenary session next week.
The report, moved by Committee Chairman Elmar Brok, underlines that Croatia, with 4.5 million inhabitants, does not burden or overstretch the EU's integration capacity.
The process of Europe's unification cannot be complete without the accession of Croatia and its neighbouring countries, Borrell said, adding that he was talking about unification, not just enlargement.
He congratulated Mesic on the progress Croatia had made, saying that although there was a lot more to be done, the Croatian authorities were working on reforms, including economic adjustment, judicial reform, and respect for minorities' rights.
Mesic said the talks with Borrell addressed the reforms in Croatia and that he informed Borrell of the situation in the region.
"I thank the European Parliament for everything it is doing so that Europe's southeast could join the EU as soon as possible. For the Union to function it must carry out certain institutional reforms, not because of Croatia, but because of itself. Croatia must carry out its own reforms, adopt standards and meet conditions, but not for the Union's but its own sake," said Mesic.
The talks with Borrell marked the start of Mesic's two-day visit to Belgium.