Tensions were rising Saturday as defiant doctors were set to hold a mass rally over the weekend in protest against the government plan to increase medical school admissions, with no sign of a breakthrough amid growing risks of a major medical disruption.

The Korea Medical Association, the largest doctors' lobby group, plans to stage a large demonstration in western Seoul on Sunday in a show of resistance against the government's plan to add 2,000 more seats to the medical school admission quota starting next year.

Some 20,000 doctors are expected to take part in the rally, the KMA said.

The government is intensifying the pressure on the striking doctors, with the filing of a criminal complaint against some former and incumbent KMA officials in a clear warning that it will not hesitate to take legal action if the strike continues.

On Friday, the police conducted raids on homes and offices of the KMA officials on suspicions of encouraging the trainee doctors to walk off the job en masse and abetting the strike.

The government had made the final plea to the junior doctors to return to work by Thursday, or they will face punishment, including the suspension of licenses.

The government's appeal has done little to bring the interns and residents back to the hospitals. As of Thursday afternoon, 565 of 9,510 striking doctors had returned, representing only about 6 percent.

The Ministry of Health and Welfare has posted a public notice on its website ordering about a dozen striking doctors taking the lead in the walkout to return to work, a move seen as a precursor to begin the process for penal action.

The government is expected to wait until the end of the weekend for more doctors to return before taking steps for punitive measures. Friday was a public holiday in South Korea.

Doctors are subject to suspension of their medical licenses for up to a year, or could face three years in prison or a fine of 30 million won ($22,455), for not complying with such government orders.

The strike, which began Feb. 20, has caused disruptions at major general hospitals across the country, leading to cancellations and delays in surgeries and other critical treatment.

The government is pushing to increase the physician numbers as a way to resolve the shortage of doctors in rural areas and essential medical fields, such as pediatrics and neurosurgery, and also given the super-aging population.

Doctors say the quota hikes will undermine the quality of medical education and other services and result in higher medical costs for patients. They have called for measures to first address the under-paid specialists and improve the legal protection against excessive medical malpractice lawsuits.