At a press conference in Przewodow, Poland, where a missile killed two people on Tuesday, Polish President Andrzej Duda said.
Polish President Andrzej Duda has expressed understanding of Ukraine’s plight after he visited the border village of Przewodow, where a missile landed on Tuesday.
“It is a hugely difficult situation for them and there are great emotions, there is also great stress,” Duda said.
According to preliminary investigations, the rocket which killed two people was most probably fired by a Ukrainian air defence system to counter Russian bombardment.
However, Duda stressed that Ukrainian officials will need to follow international law if they want access to the investigation.
"If Ukrainian guests want to see the procedural actions of the investigation, we will be able to show them as I was shown them, but as for participating in it, giving them access to documents and information, this requires a concrete legal basis, including international laws and agreements," he said.
"The search will last perhaps a dozen hours, as investigators and specialists are still extracting missile fragments and collecting evidence from the area where the accident happened.
"For the time being, no evidence of a second missile on Polish territory has been found.
"As I said, we are sure -- and all indicators show that it was a terrible and tragic accident," he added.
Villagers express their shock
Meanwhile, villagers have expressed their shock after experts discovered the rocket was "most probably" a Russian-made missile, dating back to Ukraine's membership in the Soviet Union.
"I am afraid. I haven't slept all night," said resident Joanna Magus. "I hope it's a stray missile. If it's not, we are helpless," she added.
Reflecting on Tuesday's blast, Magus said, "First I heard a terrible explosion so I quickly ran to the window and saw a huge black fireball rising into the sky above the site and then white smoke. Then the smoke started to fall slowly. A little later I saw people running and I was sure something bad had happened."
The director of the local school, Ewa Byra, told reporters that one of the victims was the husband of the school's cleaner, while the other was the father of a former pupil.
"We rather didn't expect this kind of event even though accidents happen, especially when there is war six kilometres from our village. This kind of accident can happen at any time," she said.
Poland, a NATO member, is protected by the alliance's commitment to collective defence - enshrined in Article 5 of its founding treaty - but, its response to this strike will likely be influenced by the conclusion of the investigation if the strike was accidental or intentional.
The US and NATO are so far supporting Warsaw's claims that the incident was likely an accident.