BRUSSELS, Feb. 23 (Xinhua) -- It will be "really difficult" for the European Union (EU) leaders to agree on the post-Brexit multiannual EU budget this year, European Council President Donald Tusk said Friday.

Tusk made the remarks at a press conference after a summit of the 27 EU leaders excluding the British prime minister in Brussels.

"We agreed that we should aim at speeding up the work, as compared with the previous negotiations. But finding an agreement in the European Council already this year seems really difficult," he said.

Though budgetary negotiations are always difficult, Tusk said this time all the leaders approached the budget issues with "open minds", rather than "red lines".

EU leaders has agreed to spend more on stemming illegal migration, on defense and security, as well as on the Erasmus+ program. Many leaders stressed the continued importance of cohesion policy, the Common Agricultural Policy, investments in research and innovation, and pan-European infrastructure.

"It is clear that the priorities are linked with the size of the budget, and in this context we need to address the revenue gap caused by Brexit," Tusk said.

"Despite usual differences, all leaders are ready to work on the modernization of the EU budget and its policies. And many are ready to contribute more to the post-2020 budget," he said.

It is estimated that Britain, as a net contributor to the EU budget, will after its exit leave a shortfall of more than 12 billion euros (14.7 billion U.S. dollars) per year in the budget. With its current seven-year budget period ending in 2020, the EU's executive arm European Commission (EC) plans to present the blueprint of the next multi-year budget in May.

At the informal summit the heads of state and government also discussed the post-Brexit composition of the European Parliament and appointment procedure for the EU's top jobs.

Leaders broadly supported the idea that fewer member states should mean fewer seats, which means reducing the number of MEPs from 751 to 705, Tusk said.