Foreign Minister Edgars Rinkevics, who has just concluded a working visit to Ukraine, said in a statement: "It is essential that the pro-Moscow forces that control the greater part of the territory do not prevent a speedy international investigation".
If the forces of the breakaway 'Donetsk People's Republic' were found to have shot down the airliner, then "all Ukrainian separatist forces should be considered as terrorists", he warned on LTV's evening news bulletin.
"There are a lot of unanswered questions [such as] how such a rocket system could have come into the hands of these separatists or terrorists," Rinkevics said in reference to reports that the plane may have been shot down using a sophisticated air defense system.
Earlier in the day while speaking in Dnipropetovsk, Rinkevics told municipal officials: "Latvia will continue to support Ukraine via the EU, UN and other international organizations."
President Andris Berzins also expressed his "deepest sympathy" for those who lost loved ones in the crash and echoed Rinkevics' call for a swift international investigation.
Up to 295 people are believed to have died when the Malaysia Air Boeing 777 airliner came down near Grabova in eastern Ukraine.
An hour ago terrorists in Donbas claimed that they have shot down a plane, it was insane to provide them with antiaircraft missiles #MH17— Edgars Rinkēvičs (@edgarsrinkevics) July 17, 2014