South and North Belfast and Upper Bann could be included in a new, wider unionist pact for the general election, party sources have suggested.
The DUP and Ulster Unionists plan to meet in the next few days amid speculation they could expand the four-constituency deal from the last national poll two years ago.
In 2015 a pan-unionist pact saw the DUP take back East Belfast from Alliance's Naomi Long.
The arrangement between the DUP and the UUP resulted in the latter regaining a foothold in Parliament by winning seats in Fermanagh-South Tyrone and South Antrim.
Now some suggest a new deal could help protect DUP MPs David Simpson in Upper Bann and Nigel Dodds in North Belfast, and help win South Belfast for unionism from the SDLP's Alasdair McDonnell.
The four-constituency pact at the last election also involved Newry and Armagh, where former Ulster Unionist deputy leader Danny Kennedy stood.
DUP MP Sir Jeffrey Donaldson said the negotiations did not have to include a formal pact but could amount to co-operation for specific seats. Both he and Fermanagh-South Tyrone MP Tom Elliott said their parties hoped to arrange a meeting in the next few days.
Sir Jeffrey also signalled his party could be prepared to go further than before.
The DUP MP highlighted South Belfast, where he said an agreed unionist candidate could gain a seat from nationalists, and added that March's Assembly election showed the DUP was the constituency's largest party.
"It's not just a question of the Union, it's also important to maximise our representation at Westminster to ensure Northern Ireland gets the best deal on Brexit and other issues," he said.
An Ulster Unionist source said Upper Bann - where Jo-Anne Dobson lost her Assembly seat last month - had been included in discussions on the election equation in the past.
Mr Elliott said he hoped talks with the DUP would secure the "best agreement around some constituencies", including his own.
"That shouldn't be a shock. There is no point in electing people to Westminster who will not take their seats," the Ulster Unionist MP said.
Mr Elliott conceded that it would be "very difficult" for him to hold onto Fermanagh-South Tyrone without an arrangement in place with the DUP.
Yesterday the SDLP rejected any suggestion of a nationalist pact with Sinn Fein.
South Down MP Margaret Ritchie said: "We don't do electoral pacts. The SDLP fights the election - each and every election - on our own mandate and our own basis."
But Sinn Fein MLA Declan Kearney said parties opposed to Brexit and Tory austerity should work together.
He said Sinn Fein shared much "common ground" not just with the SDLP, but also Alliance and the Green Party, on equality and dealing with the legacy of the Troubles.
Alliance said it will not be entering into any electoral pacts for the Westminster race. "We are standing on our own two feet and putting forward a constructive vision which we believe the public will back," Kellie Armstrong MLA said.
"Rather than denying people a choice, we want to offer them a real one - no sectarian headcounts, but rather progressive politics that creates a shared society for everyone."