British Prime Minister David Cameron said on Thursday restricting European Union migrant access to Britain's welfare system was a red line in his negotiations with the bloc, ahead of an EU summit he wants to use to launch informal talks on the issue.

Cameron, re-elected on May 7, has pledged to reshape Britain's ties with the European Union before holding an in-out EU membership referendum by the end of 2017.

He is under growing pressure to cut immigration, despite his pledges to cut it to less than 100,000, much of it from the EU and fueled by Britain's strong economy.