European officials have accused Boris Johnson of reneging on pledges to uphold the Good Friday agreement, ahead of the prime minister’s first meeting with his Irish counterpart.

Johnson will meet the Irish taoiseach, Leo Varadkar, in Dublin on Monday at a tumultuous moment in the Brexit process, with only 52 days until the UK’s departure. Talks are set to be tense as fears grow in Dublin and Brussels that the British prime minister is backsliding on promises to protect the tightly knit economic and social links on the island of Ireland.

“The commitment to all aspects and all the provisions of the letter and spirit of the Good Friday agreement recently seems to be taken more lightly than before,” a senior diplomat from a continental member state told the Guardian. “This avoidance of the hard border, it is not just a desire, it is not just about preferences, it is legal obligation.”

A senior official working for the EU’s chief negotiator, Michel Barnier, told diplomats this week that the UK had reneged on commitments to protect north-south co-operation on the island of Ireland, a key pillar of the Good Friday agreement.

Alarm bells were set off by Johnson’s recent letter to the European council president, Donald Tusk, which declared his government could not endorse a commitment made by Theresa May in a December 2017 EU-UK joint report.

The Brexit secretary, Stephen Barclay, fuelled concerns that the government was seeking to back out of past commitments, when he tweeted that the government was “committed to no infrastructure on the NI border”.

Such comments were seen in Brussels as “meaningless” words that marked a significant dilution of the promise to uphold an open border. The May government pledged to protect “north-south cooperation” on the island of Ireland in the 2017 joint report, widely seen in Brussels as a landmark in Brexit talks.

North-south cooperation was a pillar of the 1998 Good Friday peace agreement and covers a swathe of policies such as transport, agriculture, health, education, environment and tourism. The vast web of cooperation means, for example, that patients and ambulances can cross the border, freshwater loughs are jointly protected and Ireland’s single electricity powers millions of homes.

Since coming to office, Johnson has vowed to get rid of the backstop, a fallback plan to avoid a hard border that would see Northern Ireland maintain many EU rules, and the whole UK stay in a customs union with the EU.

“They seem to be taking a different starting point to May,” one EU official said. “They want something completely different.”

A UK government spokesperson firmly rejected suggestions the government was not committed to the Good Friday agreement. “We are committed to the common travel area, to upholding the rights of citizens of Northern Ireland, to ongoing north-south cooperation, to retaining the benefits of the single electricity market. We remain firmly committed to peace in Northern Ireland and the Belfast agreement.

“The Belfast/Good Friday agreement neither depends upon, nor requires a particular customs or regulatory regime. The broader commitments in the Belfast/Good Friday agreement include parity of esteem, partnership, democracy and a peaceful means of resolving differences. This would be best met if we could explore solutions other than the backstop.”

“We have been clear that we are happy to accept a legally binding commitment not to put infrastructure, controls or checks at the border. We hope the EU do likewise.”