JERUSALEM -- 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 a judicial overhaul that critics fear endangers 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.

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.

A reservist was fined 1,000 shekels (US$270) and another was given a suspended 15-day jail sentence for not heeding call-ups for training, the military said, in what Israeli commentators described as its first disciplinary actions during the protest.

Opposition leader Yair Lapid asked protesting reservists to hold off pending any Supreme Court ruling on appeals against the new law. Both a political watchdog group and the Israel Bar Association have filed challenges.

The crisis has opened a deep divide in Israeli society, hitting the economy hard by triggering foreign investor flight, weakening the shekel and prompting a threats of a general strike by the Histadrut public sector union.

It has also 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.

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.

Association chairman Zion Hagay said the strike was needed to discourage emigration by doctors angered by the legislation. "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.

Video circulated on social media showed the curtain-call of a popular musical in Tel Aviv, with audience members heckling or applauding a cast member as he read a statement on the crisis and a fellow actor striding off stage in apparent exasperation.

VIOLENCE IN WEST BANK, HEZBOLLAH ON PATROL

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 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 hospitalization 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 defense minister said.

The Palestinian Islamist group Hamas claimed its gunmen were the three killed near Nablus, and confirmed they died in a clash with Israeli troops.

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, an area controlled by the Iran-backed Hezbollah.

A Lebanese source familiar with the development said the men were members of a Hezbollah elite unit on a patrol that had nothing to do with Israel's domestic crisis. Hezbollah's media office said it had no comment.

Hezbollah leader Hassan Nasrallah on Monday said Israel's domestic crisis showed it was on a "path of collapse and fragmentation."

Finance Minister Bezalel Smotrich, in comments to Army Radio, said the military "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."

(Reporting by Dan Williams, Ari Rabinovitch and Henriette Chacar in Jerusalem; Andrew MacAskill in London; Laila Bassam in Beirut; writing by Dan Williams and Tom Perry; editing by Andrew Cawthorne and Nick Macfie)