European Union plans to destroy the boats of smugglers bringing desperate migrants across the Mediterranean and share the refugee burden more evenly have come under fresh fire from within and outside the EU.

In an effort to help manage more than 80,000 people who have landed on European shores so far this year, mostly in Italy and Greece, the EU's executive Commission is proposing to relocate thousands of refugees to other member countries and wants to launch a security operation in the Mediterranean to eliminate the trafficking operations.

On a visit to EU's headquarters, UN secretary general Ban Ki-moon expressed doubts about the boat destruction plan and said "the priority should be given to life-saving and strengthening search and rescue".

Mr Ban was also cool towards any EU security operation that would hunt down smugglers in Libyan territorial waters, describing the idea as "limited".

"We need to address all of this in a comprehensive way," he told reporters.

The EU is seeking legal backing for the security operation in the form of a UN Security Council resolution. It would also require the support of Libya.

Meanwhile, the Polish government voiced opposition to the Commission's proposal that it accommodate more than 2,600 refugees from Syria and Eritrea.

"Poland wants to accept (refugees), but we don't want to agree to specific numbers," government spokeswoman Malgorzata Kidawa-Blonska said.

The refugee relocation plan involves sharing 40,000 refugees in total who land in Italy and Greece. Under a weighted index based on economic strength, unemployment rates and past investment on migration, Germany, France and Spain would take in the biggest numbers.

Polish interior ministry spokeswoman Malgorzata Wozniak said that "member countries should independently decide how many refugees they are able to accept".

EU nations can still veto the plan. Interior ministers are due to discuss it at their next meeting in Luxembourg on June 15-16.