Here’s the very latest on the too-close-to-call 3rd District Democratic primary

Lori Trahan speaks to supporters Tuesday night. —Josh Reynolds for The Boston Globe

BOSTON (AP) — Only a few dozen votes separated the top two finishers in a 10-way Democratic primary for an open U.S. House seat in Massachusetts, making a recount appear increasingly likely.

Unofficial returns from 100 percent of the precincts in the congressional district showed Lori Trahan leading Dan Koh by just 52 votes, out of approximately 85,000 votes cast on Tuesday.

On Wednesday, the Massachusetts Secretary of State ordered all ballots impounded and locked away to sealed to protect against any tampering in anticipation of a recount in the too-close-to-call election.

Democratic U.S. Rep. Niki Tsongas, the widow of former U.S. Sen. Paul Tsongas, is retiring at the end of this term following more than a decade in the House. Her departure set off a scramble among Democrats in the district which stretches from the cities of Lowell and Lawrence in the Merrimack Valley to historic Concord and other towns west of Boston.

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Trahan, who served as chief of staff to former Democratic U.S. Rep. Marty Meehan, claimed victory before supporters early Wednesday.

‘‘I am deeply grateful to all who were part of making this incredible night possible. Thank you to everyone who believed in this campaign and everything it stands for,’’ she said on Twitter.

But Koh, the former chief of staff to Boston Mayor Marty Walsh, quickly made it clear he had no intention of conceding, noting that possibly hundreds of provisional ballot had yet to be counted.

‘‘It’s clear that the final outcome of the election will not be known for a few days,’’ the campaign said in a statement. The campaign also said it was reviewing procedures for a recount, should it be necessary.

State law allows candidates to request a recount if the margin of victory is less than 0.5 percent. Both Trahan and Koh had 21.6 percent of the totals votes cast.

Should either or both candidates petition for a recount, they must gather certified signatures of at least 500 registered Democrats within the district by 5 p.m. on Friday.

The eventual nominee will face in the general election Republican Rick Green, who said in a statement Wednesday he hoped for a quick resolution of the Democratic contest.

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‘‘If it devolves into a power struggle between two political dynasties, the victim will inevitably be the will of the people,’’ said Green, who was unopposed in Tuesday’s GOP primary.

Mike Mullen, an independent, will also be on the fall ballot.