Argentine President Cristina Kirchner is to undergo surgery Tuesday for complications related to a head injury, amid uncertainty over who is in charge while she recuperates.
Kirchner, 60, was greeted with encouraging words from supporters Monday, television footage showed, as she entered a Buenos Aires medical center for further testing.
She was hospitalized overnight to await surgery, the Fundacion Favaloro hospital announced in a statement.
The president had suffered a blow to the head on August 12, but it wasn't until Saturday that doctors detected a "chronic subdural hematoma" - a type of brain bleed - and ordered her to take a month's rest.
Further symptoms, including a "transitory and slight" loss of muscular strength in her left arm on Sunday, prompted doctors to order surgery to drain the blood.
Vice President Amado Boudou pledged to keep the government running, though he has not officially assumed the presidency.
"As the president asked us, we are going to maintain the administration," Boudou said earlier Monday as he took her place at a ceremony at the Casa Rosada, Argentina's presidential palace.
But he did not specify which presidential duties he will take over during Kirchner's recuperation.
The medical drama comes at a politically fraught moment, with just three weeks remaining until legislative elections in which Kirchner hopes to retain control of Congress in the middle of her second and final term.
Some 30 million Argentines are eligible to cast ballots October 27. At stake are half the seats in the lower house and a third of the senate.
Fernando Navarro, a leader of Kirchner's ruling coalition, told local radio station El Mundo the president was in "good spirits, surrounded by family," and that her condition was "not serious" and she would soon return to action.
But an opposition candidate raised concerns over the uncertainty surrounding Kirchner's medical condition.
"There is missing information," Jose Ignacio de Mendiguren told Radio La Red. "We should be getting more information about the seriousness of the issue."
Kirchner has had previous health concerns since taking office, including several bouts of low blood pressure.
And in January 2012, less than a month into her second term, she underwent surgery to remove her thyroid gland, only to be told that she had been mistakenly diagnosed with cancer.
At that time, Boudou formally assumed the presidency for 20 days.
Polls suggest the vice president has a poor public image. He is also under investigation for alleged influence peddling.
Analysts suggest this may be why he has not been officially designated to take over now.
The looming elections also make it an "inconvenient" moment to transfer power, political consultant Rosendo Fraga said on Continental radio.
"Ceding the presidency to Boudou three weeks before elections will be more unfavorable than favorable for the ruling party," he said.
Consultant Fabian Perechodnik told the same station that Kirchner's health problems "will modify the political landscape," because she has been such a dominant figure.
Kirchner has presided over rising inflation, a weakening peso and a greater government role in the economy, including unpopular controls on how many dollars people may hold.
Internationally, she has kept up her country's push for talks at the United Nations on the sovereignty of the British-ruled Falklands, which Buenos Aires claims.