Libyan authorities have detained around 450 migrants from sub-Saharan Africa.
The migrants are said to be among those hoping to make the treacherous journey to European territory.
Word of the arrests comes as European rescue teams continue searching for an estimated 900 migrants believed to have drowned following the capsizing of migrant boat off the coast of Libya over the weekend.
Adrian Edwards is with the UN's High Commissioner for Refugees.
"UNHCR now believes the number of fatalities to have been over 800, making this the deadliest incident in the Mediterranean that we have recorded. We have currently a total of about 1,300 deaths in April, this means that April of 2015 has truly been the cruellest month, the highest numbers that we have seen deaths in any month on the Mediterranean."
In response, the European Union has proposed a 10-point action plan this week to deal with the massive influx of migrants from north Africa.
Joel Millman with the International Organization for Migration is warning the death toll may end up being 10-times greater if things stay the way they are.
"IOM now fears that the 2014 total of 3,279 migrants (dead) in the Mediterranean may be surpassed this year in a matter of weeks, and could well top 30,000 by the end of this year. It could actually be even higher, but 30,000 would be almost ten times last year's death toll."
Tens of thousands of migrants have been trying to make the crossing from north Africa, particularly Libya, to the southern Italian island of Lampedusa over the past couple of weeks.
Well over a thousand of them have already perished trying to make the journey.
