DUP leader Arlene Foster has sought assurances from Leo Varadkar on the Irish government's commitment to assist the Kingsmill inquest.
Ten Protestant textile workers were gunned down during a republican paramilitary roadside ambush in South Armagh in January 1976.
An ongoing failure by the authorities in Dublin to provide Garda evidence to a fresh coroner's probe in Belfast is hampering its progress, even prompting a threat by some bereaved relatives to boycott proceedings.
The murder investigation involved police on both sides of the border, as the van used by the gunmen was stolen in the Irish Republic and later dumped there after the attack.
The Irish government has insisted legislative obstacles currently prevent it from providing the requested information to a coroner in another jurisdiction.
Garda Commissioner Noirin O'Sullivan cannot direct an officer to give evidence to the inquest without new legislation.
Law changes are being worked on in Dublin to overcome the issue.
Mrs Foster and Mr Varadkar discussed the matter during a meeting in Belfast on Friday.
"We spoke about Kingsmill and the need to bring justice to those families," she said afterwards.
"We are working with the Taoiseach in relation to those issues.
"They are looking at legislation and they are hoping to meet with the Kingsmill families before the end of the month."
The factory workers were travelling home from work when their minibus was stopped.
They were asked their religion then lined up on a country road and shot dead in a sectarian attack blamed on the IRA.
Only one man, Alan Black, survived despite being shot 18 times.