SINGAPORE -- Singapore and Malaysia are again tussling over territorial issues as Malaysia pushes to regain control of its airspace and territorial waters along its southern border.

"It is now time that we regain our control of airspace in Malaysian territory," Transport Minister Anthony Loke said at a news conference on Tuesday. "Over the years we have upgraded our air traffic control and we are capable to do so."

Citing concerns over sovereignty and the national interest, Loke said Malaysia will discuss its plans in greater detail with Singapore, and if necessary refer the matter to the International Civil Aviation Organization.

Since 1974, air traffic in southern Johor State, near the Singaporean border, has been handled by Singapore.

Loke pointed to Singapore's plan to expand Seletar Airport, the city-state's second airport, which is currently used for international charter flights, private flights, medical evacuation, maintenance, repair and overhauls, as well as airfreight.

Malaysia says Seletar Airport, located in northern Singapore near the Malaysian border, means the increase in air traffic could harm Johor's development. "We are not against Seletar Airport, but as far as the descent flight path, it cannot be over [the southern Johor district of] Pasir Gudang," Loke said.

In November, the Malaysian government rejected a plan by Malaysia Airlines' budget carrier Firefly to operate out of Seletar.

Singapore's Transport Ministry, in a statement released Tuesday, said, "The current airspace arrangements have been working well and have facilitated growth. Hence, any proposed changes will impact many stakeholders."

Singapore has simultaneously raised a separate territorial issue. The Transport Ministry said that Malaysia has extended the port boundary in the city of Johor Bahru "in a manner which encroaches into Singapore's territorial waters," and that vessels from Malaysia have repeatedly intruded.

Singapore lodged a "strong protest" with Kuala Lumpur, calling the actions "a serious violation of Singapore's sovereignty and international law," according to a ministry statement.

Its Malaysian counterpart on Wednesday rebutted that statement, calling Singapore's claims "inaccurate," and adding that Singapore has in recent years carried out extensive land reclamation in the area. Regarding its vessels, Malaysia said it is within its rights to deploy authorities and competent agencies in its territorial waters.

Singapore said Wednesday evening that the foreign ministers of the two countries had spoken by phone that day. According to a statement, Singapore Foreign Minister Vivian Balakrishnan "stressed the urgent need for Malaysia to cease these intrusions so as to comply with international law and to avoid escalating tensions on the ground."

The latest flare-up takes place amid a dispute over a water supply agreement between the neighbors. Prime Minister Mahathir Mohamad's government wants to charge a higher price for the water Malaysia ships to Singapore, which Singapore says would be a breach of contract.

The two countries got along well during the previous government of Malaysian Prime Minister Najib Razak. Since Mahathir took over the reins in May, there have been a number of irritants, including the water supply issue and postponed plans for a high-speed railway between Singapore and Kuala Lumpur.

Singapore said in its Tuesday statements that the two countries need to work together on the airspace issue, and that it wanted to resolve the maritime sovereignty matter amicably.

Asked whether there was reason to worry that the disputes could escalate, Khaw Boon Wan Khaw, Singapore's transport minister, said he hoped not. "We have so many things that we want to work together on," he said, adding, "We do not want a misunderstanding which leads to an unnecessary accident or worse, then suddenly we have a crisis to handle."

In its Wednesday statement, Malaysia said it is prepared to engage with Singapore through appropriate diplomatic channels and work toward an amicable resolution.