Boris Johnson has pledged the government’s support for Northern Ireland’s revived power-sharing executive, but sidestepped questions about funding to shore up the historic deal.

The prime minister said he felt “the hand of the future beckoning us all forward” during a visit to Stormont on Monday to support the restoration of devolution in the region after a three-year breakdown.

However, Johnson deflected questions about a promised financial package for public services and infrastructure, saying devolution was about leadership, not money.

“What’s so great about today is, as I say, that Northern Ireland politicians have put aside differences, stepped up to the plate and shown leadership,” he told a press conference after meeting party leaders.

The prime minister repeated his claim that under the Brexit deal there would be no checks on goods going from Northern Ireland to Great Britain and only minimal checks on goods going the other way. This claim has been undermined by Northern Ireland’s obligation to implement EU customs codes at its ports.

Flanked by the Irish PM, Leo Varadkar, Johnson said cooperation between Dublin, Belfast and London would deepen. “The friendship that always existed, the opportunity now is to develop even more east-west cooperation and links and that is what we are going to do,” he said.

Varadkar agreed: “The Good Friday agreement is working again. North-south cooperation is going to resume. We are going to beef up and deepen cooperation.”

However the giddy mood at Stormont, which was revived on Saturday after three years of mothballing, gave way to frustration at the lack of detail about funding.

“We are listening very carefully and we will give the support we can,” said Johnson, perhaps mindful that funding for Northern Ireland could have knock-on implications for Scotland and Wales.

Johnson sits alongside Leo Varadkar to meet the Northern Irish leaders. Photograph: Kelvin Boyes/Pool/AFP/Getty Images

Northern Ireland’s political parties signed up to power-sharing last week partly on the basis of significant Treasury transfers, with Sinn Féin mooting £1.5bn and the Democratic Unionist party floating £2bn.

Some public services, notably healthcare, are in crisis. The Northern Ireland secretary, Julian Smith, used the promise of financial support to coax Sinn Féin and the DUP towards a deal. Devolution collapsed in January 2017 amid acrimony between the two parties.

In a joint statement, Arlene Foster, the DUP leader and first minister, and Michelle O’Neill, Sinn Féin’s leader and deputy first minister, said they had had constructive meetings with Johnson and Varadkar, but stressed that funding “must follow quickly”.

“We need significant and sustained investment, not just this year but over a number of years,” said Foster. “This is crucial in ensuring transformation in areas such as health and also our road and water infrastructures.”

O’Neill said she had pressed Johnson and Varadkar over funding. “We have done our bit. I look forward to the fulfilment of the commitments made by the two governments to let us get to work.”

Foster and O’Neill were due to push the issue in a meeting with Smith on Monday night.

A botched green energy scheme nicknamed “cash for ash” that wasted hundreds of millions of pounds under Foster’s watch in the previous administration may have dented her ability to squeeze money from Whitehall.

Asked about the scandal, Johnson replied: “It is vital that public spending in Northern Ireland is properly invigilated and there is no repetition of that kind of thing.”

Johnson struck a cautious tone on the investigation of alleged crimes by military veterans during the Troubles, a contentious issue in Northern Ireland and the Conservative party.

The new power-sharing deal struck the right balance between supporting military veterans and giving victims of violence the truth, he said.

Stalled mechanisms backed by Northern Ireland’s parties in a 2014 agreement are due to be implemented as part of last week’s accord. This could set up a potential conflict with the Tory party’s recent election pledge that there would be no unfair prosecutions of armed forces personnel where there was no new evidence.

“I think that the parties here who have revived Stormont have done a very good job of finding a balance between giving people who are in search of the truth the confidence that they need but also giving people who served our country in the armed services the confidence and certainty that they need,” said Johnson.