Updated 1pm with Labour statement
The PN on Friday morning accused Abela of making a U-turn on European defence when he voted in favour of increasing defence spending.
The EU's 27 leaders on Thursday greenlit a plan drawn up by the European Commission that aims to mobilise €800 billion to "re-arm Europe" against the perceived threat from Russia.
The plan to increase defence spending was adopted unanimously, including by Malta, despite Abela earlier telling the media that more weapons would not end the war.
The prime minister said he had made Malta's position clear: "Malta will not make use of this money to buy weapons and ammunition of destruction".
But in a statement on Friday morning, the PN said in Malta, the prime minister spoke one way because it suited him politically, but did the exact opposite in Brussels.
"Abela has once again done what he is well known for – another U-turn, or rather a complete 360-degree turn, leaving Malta without direction.
"[On Thursday] morning, upon arriving at the EU summit, he stated that he was against Europe increasing its investment in defence. However, by the evening, in Brussels itself, he voted in favour of more investment in this sector."
The PN said Abela has already changed his stance on the issue three times.
"On the eve of the European Parliament elections, Abela chose to spread a blatant lie about the PN and its representatives, falsely claiming that the PN supports war. He did so simply because the PN had argued that Malta must invest more in its defence and that neutrality should be interpreted in the context of today’s realities.
"As recently as February this year, he made his first U-turn on this subject: at another EU leaders’ summit, Abela declared that Malta should invest more in defence. At that time, he even agreed with the PN that Malta cannot interpret neutrality in a static manner and must consider today’s geopolitical realities."
A month later - in comments to journalists before the EU summit on Thursday - Abela contradicted his previous position and claimed that the country should not invest more in this sector, the Opposition noted.
"Just a few hours later, Abela changed his position again. By the end of Thursday's summit, he voted in favour of the EU increasing its investment in this area."
The party said this was "classic hypocrisy", adding Malta deserved a leader who knew where he was heading.
Labour: No money for weapons or ammo
In a statement, the Labour Party said Abela had made it clear that Malta's neutrality "will not be touched".
"Although there are those who are trying to confuse minds and say that Malta has changed its position, at the end of the summit, European leaders agreed that they will respect the defence and security policy of certain member countries, in the view of their constitutional obligations, as is the case with Malta," it said.
"The Prime Minister has been, continues and will continue to stress the need to achieve peace as the solution to the war between Russia and Ukraine. He also stressed that while our country wants to protect defence and security, particularly energy infrastructure and cybersecurity, Malta will not buy weapons and ammunition, nor send soldiers to fight in wars.
"Someone else is more concerned with spending Europeans' money for arms and war, while for the Labour Government the money should be used as an investment in people and their quality of life such as health, education and the social field," the party said.