The British Northern Ireland Secretary Chris Heaton-Harris vowed to call a new Northern Ireland Assembly election after politicians could not form a local government, UK media said Friday.

Media reported earlier in the day that Northern Ireland was expected to hold new elections to the assembly, the regional legislature, after the pro-UK Democratic Unionist Party (DUP) would not join the nationality Sinn Fein party's bid to form a government after the latter won the majority back in May.

The required six-month deadline for the formulation of a government expired at 12:01 Friday local time after the two political rivals held fruitless negotiations for half a year, permitting the UK to intervene and call for new elections to be held.

The pro-UK unionists have long threatened to boycott the Sinn Fein's government after the nationalist party celebrated a historic first-ever win in the elections.

Sinn Fein has been fighting for a referendum to reunify Ireland with Northern Ireland after the north was created as a Protestant territory.

"I have limited options ahead of me. I am under a legal duty to call an election within 12 weeks," Heaton-Harris was quoted by British media outlet Sky News as saying.

Heaton-Harris has been negotiating with the parties of Northern Ireland, but unsuccessfully, the British broadcaster reported, adding that he was yet to set a date for the vote.

The DUP had lost ground among unionists due to its reaction to Brexit and North Ireland trading arrangements. This split the vote between three unionist parties. As a result, the Northern Ireland Assembly was rendered unable to elect a new speaker and form a new government, as the DUP refused to do so as part of its protest against the Northern Ireland Protocol regulating trade with the EU.

This comes after then UK PM Liz Truss and her Irish counterpart Michael Martin said the European Union and the United Kingdom may come to an agreement on the Northern Ireland Protocol, signed as part of the Brexit agreement on customs borders.

The UK government introduced in June a bill unilaterally revising the provisions of the Northern Ireland Protocol, arguing that the deal was not working, as it causes delays and interruptions to the supply chain between the United Kingdom and Northern Ireland. This incensed the EU, prompting Brussels to take legal action against the UK.

The British bill stipulates the establishment of a "green channel" for goods transported from the UK to Northern Ireland, as well as amending tax regulations, stripping the European Court of its role as the sole arbiter of disputes.

Ireland was separated into Northern Ireland and Southern Ireland by an act of parliament in 1921. In 1922, Southern Ireland became the Irish Free State, which in turn became the independent Republic of Ireland in 1948. Northern Ireland, however, remained part of the United Kingdom.