Doctors battled on Monday to save the life of former Indonesian President Suharto, who remains critically ill, while another of Southeast Asia's long-serving leaders visited his bedside.

Mahathir Mohamad, the 82-year-old former prime minister of Malaysia whose time in office overlapped Suharto's, made a short stop at the Jakarta hospital treating Suharto.

Suharto, the 86-year-old former general who ruled Indonesia for more than three decades, is still on a ventilator and doctors said his health had worsened on Sunday morning as fluid in his left lung triggered organ failure.

The head of the medical team told a news conference on Monday he was still concerned about a build-up of fluid and an infection in the lungs, but praised the former strongman ruler's resilience.

"The general condition this morning is improving. His breathing is still assisted and heart functions have also shown some improvement," said Mardjo Soebiandono, adding Suharto had shown some responses, such as opening his eyes and clutching doctors' hands, after the dosage of sedatives was briefly cut.

"He is ex-army, his fighting spirit is extraordinary," Soebiandono told reporters.

He had said on Sunday there was only a 50-50 chance Suharto could survive.

Another doctor, Muhammad Munawar, told the news conference on Monday the situation remained very serious.

"The condition is still critical, it can go up and down," he said.

Hadiarto Mangunnegoro, a lung specialist, said there were dark patches in Suharto's lungs, and he was being given antibiotics in a bid to stem infection.

LEGAL PROCEEDINGS

Mahathir and his wife left the hospital after visiting Suharto, but did not talk to the scores of journalists camped outside the hospital in south Jakarta.

But former Indonesian state secretary Moerdiono, present during the visit along with three of Suharto's daughters, said Mahathir - himself in intensive care for weeks last year after heart surgery - had whispered in Suharto's ear several times and also prayed.

Suharto, who suffered multiple organ failure on Friday and has since been on a ventilator, was visited by friend and contemporary Lee Kuan Yew at the weekend.

Lee, 84, now Singapore's minister mentor, was prime minister for decades at the same time as Suharto's rule in Indonesia. He told Singapore media he felt Suharto was not getting the honour he deserved.

Suharto's rule was marked by rapid economic growth and political stability, but at a price that included severe restrictions on human rights, as well as endemic corruption.

With Suharto in critical condition, the question of whether to continue legal proceedings against him for graft is being vigorously debated in the country.

In an apparent attempt to defuse the debate and avoid openly criticising Suharto, President Susilo Bambang Yudhoyono told a news conference on Saturday this was not an appropriate time to discuss a $1.5 billion civil case against Suharto.

Suharto was taken to Pertamina hospital on Jan. 4 suffering from anaemia and low blood pressure due to heart, lung and kidney problems.

Preparations have already been made for his burial near the Javanese royal city of Solo.

Suharto rose to power after an abortive 1965 coup officially blamed on the communist party. Up to 500,000 people were killed in anti-communist purges in the months that followed.

After Suharto quit office, he was charged with embezzling hundreds of millions of dollars of state funds, but authorities later dropped the criminal case due to his poor health.