Israeli doctors began a 24-hour strike and black ads covered newspaper front pages on Tuesday in a furore over the hard-right government's ratification of the first part of judicial reforms that critics fear endanger independence of the courts.

The bill curbing Supreme Court review of some government decisions passed in a stormy Knesset parliament on Monday after a walkout by lawmakers. Some accused long-serving Prime Minister Benjamin Netanyahu of pushing Israel towards autocracy.

With demonstrations convulsing Israel for months, thousands took to the streets and scuffled with police on Monday night.

"A Black Day for Israeli Democracy," said the ad on the front of major newspapers placed by a group describing itself as worried hi-tech workers.

The crisis has opened a deep divide in Israeli society and strained ties with Israel's closest ally, the United States, which called Monday's vote "unfortunate".

Britain urged Israel to maintain the independence of courts, build consensus and preserve robust checks and balances.

Protest leaders said growing numbers of military reservists would no longer report for duty if the government continued with its plans. Former top brass have warned that Israel's war-readiness could be at risk.

Opposition leader Yair Lapid asked the reservists to hold off their no-show threat pending any Supreme Court ruling on appeals. Both a political watchdog group and the Israel Bar Association have filed challenges.

The Israel Medical Association ordered doctors to strike for 24 hours around the nation, though not in Jerusalem, which is the scene of escalating confrontations.

It cited the removal of the Supreme Court's ability to overrule, on the basis of "unreasonableness", potential government involvement in decisions by Health Ministry staff.

Israel Medical Association chairman Zion Hagay said the strike was needed to discourage emigration by doctors angered by the step. "We are holding back doctors who want to quit and move abroad," public broadcaster Kan quoted him as saying.

The government was seeking an injunction compelling doctors to return to work.

CONSCRIPTION CONTROVERSY

Stoking opposition fury, Netanyahu's ultra-Orthodox Jewish coalition partners said on Tuesday they would submit legislation shoring up exemption from mandatory military service for their constituents who are studying in seminaries. But Netanyahu's Likud party said no such bill would be pursued for now.

First elected to top office in 1996 and now in his sixth term, Netanyahu, 73, is facing his biggest domestic crisis.

Casting the reforms as a redressing of balance among branches of government, he sought to calm the opposition - as well as Israel's Western allies - by saying on Monday he hoped to achieve consensus on any further legislation by November.

Complicating Netanyahu's position is a corruption trial in which he denies wrongdoing, and his weekend hospitalisation to receive a pacemaker. His religious-nationalist coalition's expansion of settlements on occupied land where Palestinians seek statehood has also weighed on relations with Washington.

In fresh violence, Israeli troops killed three Palestinian militants who opened fire on them from a car near the West Bank city of Nablus on Tuesday, Israel's defence minister said.

On another front, the Israeli military confirmed as genuine a video on social media showing masked men in commando clothing pacing through brush on the other side of the Lebanese border fence.

Israel worries that the powerful Iranian-backed armed group Hezbollah is testing its defences. Hezbollah leader Hassan Nasrallah on Monday said Israel's domestic crisis showed it was on a "path of collapse and fragmentation".

Hezbollah's media office didn't immediately respond to a request for comment.

Dogged by foreign investor flight, a swooning shekel and a threatened general strike by the Histadrut public sector union, Israeli Finance Minister Bezalel Smotrich told Army Radio: "The attempted casting of this as the end of democracy is simply false."

He brushed off opposition speculation that Netanyahu, freed of Supreme Court intervention, would fire an attorney-general whom some ministers describe as recalcitrant on the reforms.

The military, Smotrich added, "is combat-ready and will remain combat-ready" despite the protesting reservists, whom he accused of trying to "put a gun to the head of the government".