Ukrainian President Petro Poroshenko and his Russian counterpart Vladimir Putin have spoken about a possible ceasefire in eastern Ukraine where Ukrainian forces have been clashing with pro-Russian separatists.
According to the Kremlin, in a telephone conversation on June 17 Poroshenko and Russian President Vladimir Putin also discussed the deaths announced earlier in the day of two Russian state television journalists.
According to Russian media, sound engineer Anton Voloshin and correspondent Igor Kornelyuk were killed after they came under fire while covering fighting near the eastern city of Luhansk.
The Russian Foreign Ministry said the deaths demonstrated the "criminal nature" of Ukraine's military operation against pro-Russian rebels and urged authorities in Kyiv to investigate.
The Organization for Security and Cooperation in Europe (OSCE), whose special monitoring Mission is working in eastern Ukraine, echoed the call for a probe into the attack.
"This death is yet another horrid reminder that not enough is being done to protect journalists who risk their lives reporting from conflict zones in Ukraine," Dunja Mijatovi, the OSCE representative on media freedoms, said in a statement.
The UN Security Council called for an investigation into violence against journalists in Ukraine and expressed concern about the detention and harassment of reporters.
Reporters Without Borders said the violence affecting journalists in Ukraine had reached "unprecedented levels" and called for a "full and impartial investigation" into the two deaths.
A third member of the Russian TV crew, cameraman Viktor Denisov, survived the attack on the rebel roadblock where they were filming.
Elsewhere, Ukraine said it was treating an explosion on a pipeline carrying Russian gas to the rest of Europe as a possible "act of terrorism."
The Interior Ministry issued a statement which described the blast, which sent a plume of dark smoke high into the sky over central Ukraine, as "the latest attempt by the Russian side to discredit Ukraine as a partner in the gas sector."
The blast caused no casualties and did not interrupt gas flows.
The Urengoy-Pomary-Uzhgorod pipeline, which was hit by the blast, is the main transit route for Russian gas to the EU via Ukraine.
It comes after Russia cut supplies to Kyiv in a price row but continued supplying the European Union.
Based on reporting by AFP, Reuters and Itar-Tass