"The Ukranian security service, prosecutor's office, police and migration service have blocked several channels for the transit of foreign fighters to the IS international terrorist group through our state's territory," the Security Service of Ukraine (SBU) said in a statement.
The discovery was made in a wave of security sweeps across several major cities.
The SBU said an apartment in the government-held northeastern city of Kharkiv was being used as a temporary shelter by alleged IS members who intended to travel to both Syria and Iraq.
"Two of them had been earlier deported from Turkey in connection with their involvement in terrorist activity."
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The SBU said they held several fake passports from various countries and two of them had been waiting to receive forged Ukrainian documents so they could enter Syria through Turkey.
The Ukrainian service said the four were being financed and assisted by foreign countries but did not reveal which ones.
"Two of the foreigners have already been expelled from the territory of our state," the SBU statement said.
"Investigations into the other two are continuing."
It said that security agents had detained another "IS supporter" in the Kiev region who had undergone training in "Syrian terrorist camps".
The unnamed individual is facing a court hearing and has not yet been charged.
Ukraine has been riven by a 27-month pro-Moscow insurgency in its industrial east that has claimed the lives of more than 9,500 people and left around 400 kilometres of its southeastern border with Russia under rebel control.
Ukraine's security service has been under pressure to show its strength as the pro-Western government in Kiev tries to meet President Petro Poroshenko's pledge to apply for EU membership by 2020.
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