UK Northern Ireland Secretary Brandon Lewis on Monday called on all parties in the province to form a new power-sharing government in Belfast, after historic elections and despite unresolved Brexit disputes.
All five main political parties were due to meet Lewis for talks at the devolved legislature in Belfast, on their first day back in the job since Sinn Fein won Thursday's vote.
The nationalists, formerly the political wing of the IRA, ended a century of dominance by pro-UK unionists to become the biggest party in Northern Ireland.
The win allows Sinn Fein to nominate the symbolic position of first minister but the DUP, which came second, said post-Brexit trading arrangements need to be addressed first before it joins a new executive.
Lewis urged "a stable and accountable devolved government" in Northern Ireland and said all parties should "fulfil their responsibilities and form an executive as soon as possible".
"We have to address the outstanding issues relating to the Northern Ireland Protocol and we want to do that by agreement with the EU, but as we have always made clear, we will not shy away from taking further steps if necessary," he added.
The Democratic Unionist Party collapsed the last assembly in February by withdrawing its first minister because of its opposition to the Northern Ireland Protocol.
The arrangement, signed as part the UK's exit from the European Union, provides sweeping checks on goods heading to Northern Ireland from the British mainland and keeps the province largely under European trading rules.
The DUP fears that by creating an effective border in the Irish Sea, Northern Ireland is being cast adrift from the rest of the UK and makes a united Ireland -- Sinn Fein's aim -- more likely.
Sinn Fein leader Michelle O'Neill, who is set to become first minister, tweeted that "the voters have spoken".
"No party can hold back progress. It's now time to get to work," she added as she arrived at the Stormont Assembly buildings.
Separate trading arrangements for Northern Ireland were agreed because the province has the UK's only land border with the EU.
Keeping the border open with neighbouring Ireland, an EU member, was mandated in the 1998 Good Friday Agreement that ended three decades of violence over British rule.
In Dublin, Irish prime minister Micheal Martin also urged the DUP to join the new executive and backed Brussels in its ongoing talks with London about the application of the protocol.
"I think the European Union has been flexible, has demonstrated flexibility, but every time up to now that the European Union has demonstrated flexibility, it hasn't been reciprocated," Martin told broadcaster RTE.
"I think the moment is now for both the EU and the UK... The British government wants to bring this to a conclusion."