The murder probe raises the ante in the Ukrainian government's confrontation with the U.S. and Europe, which see the various charges against Ms. Tymoshenko as politically motivated.
Earlier this month, Ms. Tymoshenko was jailed for seven years for abuse of office, a sentence widely denounced in Ukraine and the West as an attempt by President Viktor Yanukovych to permanently sideline his opponent after years of rivalry.
Ms. Tymoshenko has appealed the conviction.
On Friday, Deputy Prosecutor General Renat Kuzmin said on a Ukrainian political talk show that prosecutors were checking claims that Ms. Tymoshenko was involved in ordering and paying for the murder of lawmaker and businessman Yevhen Shcherban, who was shot and killed at an airport in 1996.
"The country and society need to know what really happened," he said.
A spokeswoman for Ms. Tymoshenko, Natalia Lysova, dismissed the allegations as "rubbish," adding that "the attempts by Yanukovych and his allies to get rid of their political opponents know no limits."
U.S. and European Union officials have pushed for Ms. Tymoshenko to be freed, and the EU has warned that her continued incarceration could ruin a planned trade and political-association pact.
But authorities have resisted, and in addition to abuse-of-office charges have announced two new criminal investigations into the former businesswoman relating to her time as head of a gas company in the mid-1990s.
She is also under investigation in two other criminal cases.
She denies all charges against her.
Political analysts say the government has continued to pile on new charges against Ms. Tymoshenko in a bid to undermine her standing in the West.
Source: The Wall Street Journal