Former Malaysian PM Mahathir Mohamad has accused his successor of surrendering sovereignty to Singapore over his handling of a bridge project.
Dr Mahathir said Abdullah Ahmad Badawi had shown Malaysia was a "country with no guts".
Malaysia began building its half of the bridge in January but abandoned it this month after failing to find agreement with Singapore.
Dr Mahathir remains a powerful force and feared enemy in Malaysian politics.
He chose Mr Abdullah as his successor but has been a frequent critic of the two-and-a-half year administration.
Dr Mahathir told reporters on returning from London: "I have promised not to interfere in politics and I have not said anything about many things which were done wrong.
"But this is the limit. To surrender your sovereignty to Singapore as if you are scared of them."
Dr Mahathir had earlier criticised the scrapping of a major rail project, a proposed trade deal with the US and the handling of the troubled Proton car company.
The bridge - a project Dr Mahathir visualised in the 1990s - seems to have been the final straw.
"I am unhappy only when you kowtow," he said. "This is our country, yet we have to seek permission from another country to build a bridge on our side. Where is the sovereignty?
"I think this is a... country with no guts."
Malaysia began building the controversial bridge without Singapore's agreement and it has been a major source of bilateral tension.
Malaysia wanted to replace an ageing 1km (0.66 mile) causeway between the two countries with a modern bridge, allowing ships to pass underneath.
It said this would ease congestion on the causeway.
But Singapore said it was concerned about the cost of the project and the impact on the environment.
It suggested a decision on the bridge issue should be part of a package deal on unresolved bilateral issues.
Mr Abdullah is currently in the Caribbean and has made no response to Dr Mahathir's comments.
PUTRAJAYA: Tun Dr Mahathir Mohamad returned from a two-week holiday in London yesterday as defiant as ever, refusing to cease disputing the Government’s decision to scrap the Johor Strait bridge project.
He said as a citizen, he had a right to do so if the country’s sovereignty was surrendered.
"If you surrender your sovereignty to Singapore ... I think this is a half-past-six country which has no guts," the former prime minister told reporters at the Kuala Lumpur International Airport on his return.
"I promised not to interfere in politics and I have not said anything about many things done which were wrong.
"But this is the limit — to surrender your sovereignty to Singapore as if you are scared of them.
"This does not speak well of your self-respect."
Asked to what extent he would pursue the matter, Dr Mahathir said:
"I cannot go to war ... I have no power."
He dismissed talk that Umno members were worried that his conflict with the present administration over the bridge issue would disunite Umno.
The bridge issue, he said, had nothing to do with disunity and was about self-respect.
Asked why he had not given his recent open letter to Prime Minister Datuk Seri Abdullah Ahmad Badawi instead of distributing it to Umno members, Dr Mahathir said:
"I did not write the letter to him. What for? Even if I talk to you (the media), it won’t see the light of day in the papers.
"Even if I were to give it to you to publish, you will not do it.
"Even if you do, Kalimullah will chop it," he said, referring to New Straits Times Press deputy chairman and editorial adviser Datuk Kalimullah Hassan.
However, Dr Mahathir described his relationship with Abdullah as "very fine and very good".
"I am unhappy only when you kowtow. This is our country, yet we have to seek permission from another country to build a bridge on our side. Where is the sovereignty?"