The workers were fighting the Ebola outbreak, which has killed nearly 1,000 people in three countries.
Johnson Sirleaf pledged up to 18 million US dollars for the Ebola fight, part of which will be given to health workers to help with insurance and death benefits, to fund more ambulances and to increase the number of treatment centres.
(READ MORE: World Bank sets emergency fund to curb Ebola)
"If we haven't done enough so far, I have come to apologise to you," she told hundreds of health workers who gathered at Monrovia's City Hall for a meeting with her government.
The West African Ebola outbreak, centred on Guinea, Sierra Leone and Liberia, is the worst in history.
The World Health Organization (WHO) said on Friday it is an international health emergency that will likely continue spreading for months.
(READ MORE: WHO declares Ebola epidemic an international health emergency)
The disease has put a severe strain on the health systems of affected states and governments have responded with a range of measures, including the declaration of national emergencies in Sierra Leone, Liberia and Nigeria, which confirmed seven cases of Ebola in Lagos.
Ebola has reaped a high toll on health workers who have acted as first responders. Liberia alone has lost at least three doctors to the virus and 32 health workers.
Sierra Leone's Health Ministry said a senior physician had contracted the disease at the Connaught referral hospital in the capital, Freetown.
Dr. Modupeh Cole contracted the disease "after treating a patient ... who was later proved to have the virus and died," said ministry spokesman Sidi Yahya Tunis.
Cole was taken to an Ebola treatment centre in eastern Kailahun district, run by medical charity Medecins Sans Frontieres, Tunis said.
He is the latest Sierra Leonean medical practitioner to contract the virus. The country's leading Ebola doctor, Shek Umar Khan, died of the disease last month and several nurses have died.
GUINEA BORDERS TO STAY OPEN
Guinea said earlier on Saturday at a news conference attended by four government ministers that it had closed its borders with Sierra Leone and Liberia to halt the spread of Ebola.
Authorities said the decision was taken primarily to prevent infected people crossing into Guinea, where at least 367 people have died of Ebola since March and 18 others are being treated in isolation.
However, state television later said the borders remained open, in an about-face that appeared to highlight the difficulties governments face in coordinating policy in the face of the fast-moving outbreak.
"Guinea has not closed its borders with Sierra Leone or with Liberia. It's rather that we have taken health measures at the border posts," the television channel said.
A government source said the minister who made the original announcement had not been in possession of accurate information.
Ebola is one of the deadliest diseases known to humanity. It has no proven cure and there is no vaccine to prevent infection.
The most effective treatment involves alleviating symptoms that include fever, vomiting and diarrhoea.
The rigorous use of quarantine is needed to prevent its spread, as well as high standards of hygiene for anyone who might come into contact with the disease.
These measures have proved hard to enforce given that Ebola has spread in rural parts of some of the world's poorest countries. The task is made harder because of mistrust of health workers in areas with inadequate public health services.
FRESH EBOLA TESTS
The WHO said on Friday 961 people have died during the outbreak and 1,779 have been infected. The infections and deaths have led to tests on suspected Ebola cases around the world.
(READ MORE: UPDATE: Uganda tests first possible Ebola victim)
Authorities in Ghana said they were testing samples from a man from Burkina Faso who died while being transported to hospital in the Upper East region.
"He had fever and was bleeding from the nose so we are testing him for Ebola because we don't want to take chances," Yaw Manu, medical head at Bawku Presbyterian Hospital, said by telephone.
Ghana has previously conducted about 20 Ebola tests, though none has proved positive.
Test results for a patient being treated in a Toronto-area hospital for a suspected case of Ebola are due within 24 hours, Ontario's health ministry said on Saturday. The patient recently came to Canada from Nigeria.
Authorities in Benin also said they were testing a patient for Ebola, the second suspected case in the country, while Saudi Arabia's Health Ministry said initial tests on a dead Saudi citizen suspected of having Ebola were negative.
International alarm over the spread of the disease increased last month when a U.S. citizen died in Nigeria after travelling there by plane from Liberia. Since then, other countries with no cases of the disease have taken measures as a precaution.
(READ MORE: Containing the Ebola virus)
Zambia said it would restrict the entry of travellers from countries affected by the virus and would ban Zambians from travelling to those countries, in one of the strictest actions by any nation outside of West Africa.
Zambia's Health Ministry also advised against holding any "international events" such as conferences and other gatherings, citing concerns about controlling potential outbreaks.
Gambia's Ministry of Transport said any planes flying to the capital, Banjul, should not pick up passengers at airports in Conakry, Freetown or Monrovia.
(READ MORE: Africa needs to look inward to tackle Ebola)