On the Malaysian side, Transport Minister Anthony Loke on Wednesday morning issued a full-throated statement countering Singapore’s claim that his country had violated the Lion City’s sovereignty by unilaterally altering boundaries around a port in the southern state of Johor.

Loke claimed Singapore’s position was wrong because it had judged its maritime boundary based on “basepoints” on reclaimed land.

“It is trite law that land reclamation does not extend a state’s basepoints and/or baselines,” Loke said in a statement to the media. “As such, the altered port limits of Johor Bahru are in Malaysia’s territorial sea and it is well within Malaysia’s right to draw any port limit in our territorial sea in accordance with our national laws.”

The Singapore statement on Wednesday disputed this account, pointing out that the new Johor Bahru port limits extended beyond Kuala Lumpur’s territorial sea claim set out in a 1979 Malaysian map that the city state had never accepted. The two countries acrimoniously split in 1965.

The Malaysian minister meanwhile pushed back against Singapore’s complaints that Malaysian maritime enforcement vessels had stepped up activity in the disputed area over the last two weeks.

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Singapore’s transport ministry had said such actions hurt bilateral ties and that the republic would not hesitate to safeguard its sovereignty.

Loke countered, taking issue with a Singaporean circular that asked civilian vessels to ignore Malaysia’s new port boundaries, as well as purported intrusions by the city state’s vessels into the area.

“It is precisely these actions by Singapore that amount to serious violations of Malaysia’s sovereignty and international law and are unconducive to good bilateral relations, cause confusion for the international shipping community, and lead to increased navigational and safety risks to all parties,” the minister said.

In Singapore, the transport ministry sought to show the Lion City was not unreasonable in its approach to another dispute made public on Tuesday – over airspace in Malaysian territory administered by the city state’s air traffic controllers.

Loke, in a briefing with reporters on Tuesday, said Singapore had “just recently” notified the Malaysian side of its plans to broadcast a radar system that would require planes landing in a secondary civilian airport to make their landing approach over Johor – inconveniencing residents and port activity there.

But Singapore late on Tuesday revealed talks between both sides on the matter had in fact been ongoing since last December, with correspondence taking place before and after the May 9 election in which Loke’s Pakatan Harapan coalition took power.

The Singaporean transport ministry released meeting minutes and emails to prove its position.

Both sides continue to emphasise they were keen to resolve the differences through negotiations.

Singapore media quoted Transport Minister Khaw Boon Wan as saying the country would use “standard rules of engagement” if it were intruded.

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“We do not want a misunderstanding which leads to unnecessary accident or worse, then suddenly we have a crisis to handle … we hope that good sense prevails,” Khaw said.

In both countries, the commentariat and ordinary citizens alike were on Wednesday still digesting how ties had suddenly turned fraught overnight.

There was no sign that the neighbours were at loggerheads before Tuesday’s revelations, and Malaysian Prime Minister Mahathir Mohamad and his Singaporean counterpart Lee Hsien Loong in November pledged to strengthen the bilateral ties after a meeting.

Theories abounded on the reasons for the diplomatic low point, with some heavyweight voices suggesting it had to do with Mahathir – the second-time prime minister who took a hawkish approach to the Lion City during his first stint in power.

“Looks like some countries are back to their old tricks and games to bolster their own positions. Let’s stand firm. Let’s stand united. Majulah Singapura,” Singapore parliamentary speaker Tan Chuan-Jin wrote on his Facebook page, citing the republic’s national motto.

Bilahari Kausikan, a vocal, retired Singaporean diplomat, suggested his country was being used by Mahathir’s seven-month old government as the spectre of an external threat as it comes under pressure at home.

“Political uncertainty in Malaysia inevitably leads to Singapore being used as a bogeyman to hold things together,” Bilahari wrote on Facebook.

He said the “intrinsically unstable” Pakatan Harapan coalition was being “held together” by 93-year-old Mahathir. “Wish the good doctor good health and long-life: it may well be worse without him.”

There were no such veiled digs from the Malaysian side.

Mahathir on Wednesday morning offered local reporters a measured response when queried about Singapore’s claims about Malaysian incursions into its territorial waters.

“We can measure to see if it is true or not but we had not touched their border … we are still within our waters,” he was quoted as saying.