Economic migrants rescued from the Mediterranean while trying to reach Europe should be returned home, Home Secretary Theresa May has suggested.
Offering resettlement regardless of circumstances would encourage more to make "perilous journeys", she said.
This was why the UK was not backing a resettlement quota plan, she added. The European Commission is due to publish plans to deal with the crisis.
A UK warship rescued about 450 people from the Mediterranean on Wednesday.
The UN estimates that 60,000 people have already tried to cross the Mediterranean from North Africa this year.
More than 1,800 migrants have died - a 20-fold increase on the same period in 2014.
France, Germany, Italy and some other countries have backed the quota proposal, but a majority of EU governments would have to agree for it to become law.
As things currently stand, the UK could decide to opt in to the scheme, but could not be compelled to join, as it has the power to opt out of justice and home affairs policies set by the EU - and asylum decisions are included in that opt-out.
The Home Office has instead urged the EU to focus on combating people traffickers.
Chris Morris, the BBC's Europe correspondent, says the Commission's draft proposals speak of a determination to implement "a more swift return system" and to "ensure a humane and dignified treatment of returnees, and a proportionate use of coercive measures".
It wants to strengthen the role of the border agency Frontex to help individual member states send people back to their countries of origin.
The Commission's stance should be taken to mean that due legal process will be observed, our correspondent added. Once that has been done, the Commission wants more rejected applicants to be sent back.
Mrs May wrote in the Times: "The present situation in the Mediterranean is intolerable.
"Gangs are profiting from the misery of their fellow humans, selling them false promises before loading them on to dangerous vessels and sending them - in many cases - to their deaths.
"This problem is not new but it is growing. It demands a clear response from European nations."
She added: "We cannot do anything which encourages more people to make these perilous journeys - or which makes it easier for the gangs responsible for their misery.
"That is why the UK will not participate in a mandatory system of resettlement or relocation."
Mrs May said there was a need to distinguish between those fleeing persecution and economic migrants crossing the Mediterranean in the hope of a better life.
"We must not provide new incentives for those simply seeking to come for economic reasons," she wrote.
Mrs May added that the EU should work to establish safe landing sites in North Africa, "underpinned by an active programme of returns".
There also needed to be "a properly structured programme" which slowed people travelling through transit countries and encouraged them to return to their country of origin or to countries other than in Europe.
Mrs May said she disagreed with the suggestion by the EU's High Representative, Federica Mogherini, that "no migrants" intercepted at sea should be "sent back against their will".
"Such an approach would only act as an increased pull factor across the Mediterranean and encourage more people to put their lives at risk."
Mrs May also told BBC Radio 4's Today programme that many of the people coming across the central Mediterranean were not refugees, but economic migrants from places such as Nigeria, Eritrea and Somalia.
She went on to say that the UK was helping refugees from Syria by donating £800m in aid, making it the second biggest bilateral donor.
The UK has deployed a warship - HMS Bulwark - and search-and-rescue helicopters in the waters between Libya and Italy.
The Home Office says the ship was alerted to four craft in potential distress approximately 40 miles off the coast of Libya on Wednesday, before taking hundreds of people on board.
Defence Secretary Michael Fallon, said: "HMS Bulwark and her crew have already proved an invaluable asset in assisting with the Mediterranean migrant crisis.
"Including today's events the Royal Navy will have rescued about 600 people since starting operations at the beginning of the month."
Sandro Gozi, an Italian MP who is Italy's under secretary for European affairs, also told Today that EU member states needed to share responsibility for the "crisis" in the Mediterranean.
"This is essential for the European Union, and only through common policy on immigration and asylum can we give an efficient response to such a huge problem.
"We appreciate a lot the work that the UK government is doing at UN level, because there is a need to fight against the smugglers.
"It is up to the UK to decide whether to opt out or not from the system we are building, remembering that when you opt out from a decision, you opt out also from the debate, and you opt out from how to shape new policies."