The United States Senate has taken the first steps towards reopening the Department of Homeland Security, after approving a budget framework that would fund immigration enforcement agencies, despite opposition from the Democrats.

The department has been partially shut down since mid-February, after Democrats demanded policy changes following the fatal shootings of two protesters, Renee Good and Alex Pretti, by federal agents in Minneapolis in January.

The Senate voted 50-48 early on Thursday morning to advance the plan, which would provide funding for Immigration and Customs Enforcement (ICE) and the Border Patrol. The measure now moves to the House of Representatives.

ICE, the federal agency responsible for immigration arrests, detentions and deportations in the US, has long been controversial, particularly during President Donald Trump’s “America First” immigration crackdown.

Human rights groups have accused officers of carrying out aggressive street arrests, separating families and targeting undocumented migrants, while Democrats have repeatedly pushed for tighter oversight of the agency.

Senate Majority Leader John Thune said Republicans were determined to secure funding for border enforcement. “We have a multistep process ahead of us, but at the end Republicans will have helped ensure that America’s borders are secure and prevented Democrats from defunding these important agencies,” Thune said.

To pass the bill, Republicans are using a process known as budget reconciliation to pass the funding measure. It allows some budget-related legislation to pass the Senate with a simple majority, rather than the 60 votes usually needed to overcome a filibuster – a Senate rule that allows lawmakers to delay or block most legislation unless 60 senators vote to move it forward. Republicans hold 53 seats in the 100-member chamber, meaning they would normally need Democratic support.

The reconciliation process can still be lengthy. It allows for extended debate and a series of amendment votes, while proposals are also reviewed by the Senate parliamentarian, a non-partisan official who decides whether measures comply with Senate rules.

Senators voted through the night from Wednesday into Thursday, with Democrats proposing amendments aimed at reducing healthcare and household costs, seeking to contrast Republican priorities on immigration.

“Instead of pumping hundreds of billions of dollars into ICE and Border Patrol, Republicans should be working with Democrats to lower out-of-pocket costs,” Senate Democratic leader Chuck Schumer said.

The Senate has already passed a separate bipartisan measure to reopen the rest of the Homeland Security Department. However, Republican leaders in the House have said they will not consider that bill until progress is made on funding ICE and Border Patrol as well.

The $70bn proposal would finance the two agencies for three years, covering the remainder of Trump’s term. Republican leaders say they hope to send the legislation to Trump for approval in the coming weeks.