Home secretary Theresa May said that the UK needs to "stand tall and lead in Europe" rather than leaving the EU, the home secretary has said.
In her first speech ahead of the referendum in June, May said that the UK needs to position itself in the centre of the EU and force change from within, but also stated that sovereignty and security are bolstered by the UK's position in the 28-member bloc.
Speaking directly on her remit as home secretary, May added that the UK is more secure from terrorism and crime due to its membership of the EU.
She added: "Now I know some people say the EU does not make us more secure because it does not allow us to control our border. But that is not true. Free movement rules mean it is harder to control the volume of European immigration - and as I said yesterday that is clearly no good thing – but they do not mean we cannot control the border.
"The fact that we are not part of Schengen – the group of countries without border checks – means we have avoided the worst of the migration crisis that has hit continental Europe over the last year.
"It means we can conduct checks on people travelling to Britain from elsewhere in Europe. And, subject to certain rules and the availability of information, it means we can block entry for serious criminals and terrorist."
Mays speech comes after she said on Sunday that free movement in the EU makes it more difficult, but not impossible, to control immigration.
However, justice secretary Michael Gove said the UK will face a migration "free-for-all" if it does not vote to leave the EU.
That in turn would put a direct strain on public services, including the NHS, said Gove, who is campaigning for Brexit.
He wrote: "Because we cannot control our borders - and because our deal sadly does nothing to change this fact - public services such as the NHS will face an unquantifiable strain as millions more become EU citizens."
"There is a direct and serious threat to our public services, standard of living and ability to maintain social solidarity if we accept continued EU membership."
Immigration remains a central issue in the EU debate, with Leave campaigners arguing that to have control the UK must leave the EU. But Remain campaigners have said that if the UK wanted to stay in the single market, it would have to accept free movement of people anyway.
Meanwhile, former Home secretary Michael Howard said that May's comments that she thought immigration was too high "but there was very little she could do about it" was a "humiliating spectacle".
Howard added that he has "no idea" how May could come to the conclusion that the UK is safer inside the EU, citing the fact the European Court of Justice blocked her from preventing a terror suspect coming to the UK.
Former work and pensions secretary Iain Duncan Smith has also seized on May's comments, saying that she has essentially accepted that immigration is "out of control".
Some have even said that there is a distinct difference to the position of Prime Minister David Cameron and the home secretary. Duncan Smith went as far to say that May has "undermined" Cameron and the government with her intervention.
Given May said that she wants to end involvement in the European Convention on Human Rights and against expansion of the EU to countries including Turkey, Duncan Smith said:
She actually basically questions the very campaign she says that she supports. This is a remarkable intervention. She has really thrown the gauntlet down and undermines the whole of the 'vote stay in' campaign.
Members of the cabinet, as well as the wider Conservative party, have clashed over the UK's membership of the EU. A number of truces having been put under pressure, most notably between Mayor of London Boris Johnson and Prime Minister David Cameron.
In the Labour ranks, Lord Peter Mandelson accused the Leave campaign, which Duncan Smith speaks for, of "hoisting the white flag" over its campaign as it failed to show how Britain would bolster trade after a Leave vote.
"This was the week when Vote Leave hoisted the white flag on arguments around the economy," he said. "First the Treasury then Barack Obama demolished their flimsy arguments about trade and prosperity and so they have turned instead to their default nationalist territory of immigration."