KIEV, Ukraine — Fighting intensified in the rebel-controlled region of Ukraine on Wednesday, with military officials reporting that two Ukrainian Su-25 fighter jets had been shot down near the village of Dmytrivka.
Few details of the latest shoot-downs were available. But before news of the downed fighter planes emerged, a spokesman for Ukraine’s National Security and Defense Council in Kiev said that the military operation to suppress the insurgents was advancing in the east, with government troops having retaken the cities of Severodonetsk and Popasna in the Luhansk region, as they continued an aggressive push from the north and west.
Officials said that rebels had blown up a road bridge, railroad bridge and train tracks in the city of Gorlivka. And they said that there was continued fierce fighting along a section of the border with Russia that remains porous. Ukrainian forces are increasingly desperate to seal that border to prevent resupplies of weapons or new fighters from entering Ukraine.
A Ukrainian military spokesman, Andriy Lysenko, said Russia had increased its troop presence along the border and that there were increasing numbers of incidents of cross-border shooting.
The downing of the two fighter jets was a serious blow to the Ukrainian military, which has limited air power.
In Kharkiv, a government-controlled city where the bodies of most of the victims of last Thursday’s crash of a Malaysia Airlines jetliner were taken, a Dutch military plane loaded with coffins left for the Netherlands on Wednesday, the first in a long series of flights to repatriate the bodies of 298 passengers and crew killed last week when a Russian-made missile downed the plane.
At a ceremony before the departure of the Hercules transport on the sun-swept tarmac of Kharkiv International Airport, Ukrainian officials and foreign diplomats mixed solemn tributes to the dead with angry demands that those responsible for the shooting down of the jet be found and brought to justice.
“This is a tragedy of unspeakable proportions,’’ an Australian representative, Angus Houston, told the gathering, flanked by a Ukrainian military honor guard dressed in black uniforms.
“Those who are guilty for this terrorist act will be punished,’’ said the Ukrainian vice prime minister, Volodymyr Groysman. He left no doubt that Ukraine believes the guilty parties are not only pro-Russian rebels into whose territory in eastern Ukraine the plane crashed last Thursday, but also Russia, asserting that “Russian military personnel launched the missile that hit a civilian Malaysian aircraft.’’
“We are today sending off innocents who were murdered,’’ he added.
Officers from the Kiev Military Academy, dressed in blue uniforms with yellow braid — the colors of the Ukrainian flag — carried four wooden coffins into the plane, which took off at noon bound for the Netherlands with 16 bodies on board, according to Dutch officials. A second plane from Australia was due to take 24 more bodies, also to the Netherlands, later Wednesday.
Although foreign officials at the ceremony called for justice, they did not assign blame. That stood in contrast to Groysman, who denounced what he called “Russian aggression’’ against Ukraine.
As the plane carrying the first bodies took off, a Ukrainian woman waved a hand-drawn sign reading “Judge Putin in the Hague,’’ a reference to President Vladimir Putin of Russia.
The woman, Alexandra Kharchenko, a 39-year-old designer who lives in Kharkiv, said the Russian president should be called before an international tribunal. She accused Putin of encouraging and arming the pro-Russian separatists whom Ukraine and the United States have accused of firing the surface-to-air missile that downed the passenger jet.
“I just want to draw attention to who is ultimately responsible for this crime,’’ Kharchenko said.
The Kremlin and the rebels have repeatedly denied any role in shooting down the Malaysia Airlines plane, which was en route to Kuala Lumpur, Malaysia, from Amsterdam, and have said the blame lies with Ukraine.
A representative for the Dutch government at the farewell ceremony in Kharkiv called for patience in assessing exactly what happened. He cautioned that even identifying the bodies — a task that will be carried out by Dutch specialists at a laboratory in the Netherlands — would be a long and laborious process.
The bodies, held for days by the pro-Russian rebels who control the crash site, were delivered to Kharkiv by rail Tuesday, along with the data and voice recorders from the doomed plane. It will take at least several days for experts to unload five refrigerated railway cars at a Soviet-era tank factory in Kharkiv, place the bodies in coffins and transport them by air to the Netherlands.
“Today your journey home begins. It will still be a long journey. We have started a process that will take time,’’ said Hans Docter, the Dutch representative. “We have to do this right. The eyes of the world are upon us.’’
In Britain, the Department for Transportation confirmed in a statement Wednesday that both the flight data recorder and the cockpit voice recorder from Malaysia Airlines Flight 17 had been delivered by Dutch investigators to the department’s Air Accidents Investigation Branch.
Representatives of the Dutch Safety Board, who have been asked by Ukraine to lead the technical investigation into the crash, received the recording devices known as black boxes from Malaysian officials who obtained them from rebels Monday and put them on the train carrying bodies to Kharkiv, a government-controlled city. The Dutch delivered them to Britain early Wednesday.
The Netherlands, which had the largest number of citizens aboard Flight 17, took formal control of the inquiry later on Wednesday, following negotiations with the governments of Ukraine and Malaysia, as well as the International Civil Aviation Organization, an arm of the United Nations.
Under international rules, Ukraine, as the country where the accident took place, would normally be first in line to lead the inquiry, followed by Malaysia, as the country in which the aircraft was registered. Both governments exercised their authority to delegate the responsibility to another country.