JERUSALEM -- Israeli Prime Minister Benjamin Netanyahu was recovering in a hospital on Sunday after an emergency heart procedure, as tens of thousands of supporters and opponents of his government's judicial overhaul plan held rival rallies ahead of a key vote.

Netanyahu's sudden hospitalization for the implant of a pacemaker added another dizzying twist to an already dramatic series of events that have bitterly divided his country and are certain to shape Israel's future. Monday's vote in Parliament is expected to approve the first major piece of legislation in the contentious plan.

Netanyahu's doctors said Sunday the procedure had gone smoothly. But by Sunday evening, Netanyahu remained in Sheba Hospital near Tel Aviv.

In a short video statement from the hospital, Netanyahu, 73, said he felt fine and thanked his doctors for his treatment and the public for wishing him well.

Wearing a white dress shirt and dark blazer, Netanyahu said he was pursuing a compromise with his opponents while also preparing for a vote on Monday that would enshrine a key piece of the legislation into law.

"I want you to know that tomorrow morning I'm joining my colleagues at the Knesset," he said.

The overhaul calls for sweeping changes aimed at curbing the powers of the judiciary, from limiting the Supreme Court's ability to challenge parliamentary decisions to changing the way judges are selected.

Netanyahu and his far-right allies, a collection of ultranationalist and ultra-Orthodox parties, say the changes are needed to curb the powers of unelected judges. Their opponents, coming largely from Israel's professional middle class, say the plan will destroy the country's fragile system of checks and balances and push Israel toward authoritarian rule.

The plan has triggered seven months of mass protests, drawn harsh criticism from business and medical leaders, and a fast-rising number of military reservists in key units have said they will stop reporting for duty if the plan passes, raising concern that Israel's security could be threatened.

U.S. President Joe Biden has called on Netanyahu to freeze the plan, and Israel's ceremonial president, Isaac Herzog, has attempted to broker a compromise between the prime minister and his opponents. Herzog, who returned Sunday from a trip to the White House, immediately rushed to Netanyahu's hospital room.

"This is a time of emergency," Herzog said. "We have to reach an agreement."

Herzog planned meetings later Sunday with Israel's opposition leader, Yair Lapid, and Benny Gantz, head of National Unity, another opposition party.

As they spoke, tens of thousands of people were gathering for mass rallies for and against the plan. Netanyahu's supporters thronged central Tel Aviv -- normally the setting for anti-government protests -- while his opponents marched on Israel's Knesset, or Parliament.

Many of the protesters in Jerusalem had camped out in a nearby park, after completing a four-day march into the city from Tel Aviv on Saturday.

After seven months of mass protests against the plan, tensions were surging as lawmakers began a marathon debate over the first major piece of the overhaul ahead of Monday's vote

In a fiery speech launching the session, Simcha Rothman, a main driver of the overhaul, denounced the courts, saying they damaged Israel's democratic ideals by arbitrarily striking down government decisions.

"This small clause is meant to restore democracy to the state of Israel," Rothman said. "I call on Knesset members to approve the bill."

Despite the attempts to project business as usual, Netanyahu's schedule was disrupted. His weekly cabinet meeting scheduled for Sunday morning was postponed. Two upcoming overseas trips, to Cyprus and Turkey, were being rescheduled, his office said.

Israeli media said last-ditch efforts were underway to find a solution out of the impasse. But it wasn't clear whether those would bear fruit.

In Monday's vote, legislators are to vote on an overhaul measure that would prevent judges from striking down government decisions on the basis that they are "unreasonable."

Proponents say the current "reasonability" standard gives judges excessive powers over decision-making by elected officials. Critics say removing it would allow the government to pass arbitrary decisions, make improper appointments or firings and open the door to corruption.

Speaking in Parliament, opposition leader Yair Lapid called for Netanyahu to resume compromise talks and lauded the protesters for standing up to the government.

"The government of Israel launched a war of attrition against the citizens of Israel and discovered the people can't be broken. We won't give up on our children's future," he said.

Orit Farkash HaCohen, of the opposition National Unity party, broke down into tears as she criticized the government. "Our country is on fire. You've destroyed the country," she said. "I can't believe what I'm seeing."

Protesters, who come from a wide swath of Israeli society, see the overhaul as a power grab fuelled by personal and political grievances of Netanyahu -- who is on trial for corruption charges -- and his partners who want to deepen Israel's control of the occupied West Bank and perpetuate controversial draft exemptions for ultra-Orthodox men.

Netanyahu was rushed to the hospital in the middle of the night a week after being hospitalized for what doctors said was dehydration.

The sudden hospitalization for the pacemaker procedure indicated that Netanyahu's health issues were more serious than what he initially said.

In a video statement, his doctors said they had implanted a device to monitor his heart after last week's health scare. When the device showed anomolies, they said he needed a pacemaker.

Prof. Roy Beinart, senior physician and director at the Davidai Arrhythmia Center at Sheba Medical Center's Heart Institute, said Netanyahu has suffered from a "conduction disorder," or irregular heart beat, for years.

"The implantation went smoothly, without any complications. He is not in a life-threatening condition," Beinart said. "He feels great and is returning to his daily routine."

Netanyahu keeps a busy schedule and his office says he is in good health. But he has come under criticism in recent days for releasing few details about his well-being or medical records over the years.

Further ratcheting up the pressure on the Israeli leader, thousands of military reservists have been declaring their refusal to serve under a government taking steps that they see as setting the country on a path to dictatorship. Those moves have prompted fears that the military's preparedness could be compromised.

Over 100 retired security chiefs publicly supported the growing ranks of military reservists who plan to stop reporting for duty if the overhaul is advanced.

"These are dangerous cracks," military chief Lt.-Gen. Herzi Halevi wrote in a letter to soldiers Sunday meant to address the tensions. "If we will not be a strong and cohesive military, if the best do not serve in the IDF, we will no longer be able to exist as a country in the region."

Netanyahu and his far-right allies announced the overhaul plan in January, days after taking office.

Netanyahu paused the overhaul in March after intense pressure by protesters and labour strikes that halted outgoing flights and shut down parts of the economy. After talks to find a compromise failed last month, he said his government was pressing on with the overhaul.