The Ukrainian parliament approved a bill against separatism on Tuesday in a bid to end violent pro-Russian rallies in the country's east regions.
According to the new law, those charged with violation of Ukraine's territorial supremacy could face a jail term of up to five years for single offence and up to 10 years for repeated offense.
Earlier, the maximum sentence for encroachment on Ukraine's territorial integrity was three years in prison.
The parliament also made the criminal liability for treason harsher, requiring offenders to spend 12 to 15 years behind the bars.
Previously, the minimum mandatory sentence for treason in Ukraine was a jail term of 10 years.
Kiev ratcheted up a fight against separatism after a series of pro-Russian rallies in eastern Ukraine, including the seizure of government buildings in the cities of Donetsk, Lugansk and Kharkov.
Crowds of armed activists demanded that referendums be held in their cities to secede from Ukraine and join Russia, following Crimea's integration into Russia last month.
On March 18, Russian President Vladimir Putin and Crimean leaders signed a treaty to make the southern peninsula part of Russian territory after almost 97 percent of Crimean voters backed splitting from Ukraine at a referendum.
Kiev has rejected the referendum and Crimea's integration into Russia as unconstitutional.