The deployment of Russian soldiers in the Crimea without any identifying markings raises questions about whether this is a breach of international law on warfare.
Jonathan Eyal, international director at the London-based Royal United Services Institute, is adamant that it is. "It is a gross violation. It is highly illegal. It is something that violates all conventions of warfare going back hundreds of years," said Eyal.
He expressed surprise that the International Committee of the Red Cross, which is closely linked with the Geneva conventions on warfare, had not commented on this.
But the Geneva-based ICRC said the situation is far from clear-cut, a view supported by some military experts who offer alternative interpretations to Eyal.
The troops taking over or surrounding key strategic positions in the Crimea are in uniform but have had badges or other forms of identification removed. But some of them have confirmed to reporters they are Russian marines from Sevastopol. Trucks and armed vehicles have had their number plates disguised too, but some of the coverings have fallen off, revealing them to from the Russian army.
Russian president Vladimir Putin, at a press conference this week, refused to confirm they are Russian regulars and suggested they were spontaneous groups who could have acquired the uniforms from army surplus stores. The newly-installed pro-Russian leader in Crimea, Sergei Aksyonov, on Wednesday night said there were 11,000 "self-defence troops", according to AP.
MPs in the Crimean parliament have announced they consider the territory to be part of Russia, providing some post-event legal cover for Russian troops involved in the take-over.
Eyal said he was surprised that more has not been made of the fact that the Russians have hidden their identity. "The basic principle in every conflict is combatants must have clear markings and they must belong to a state. If they do not belong to a state, they are classified as mercenaries or petty criminals. They are not entitled to be treated as prisoners of war," he said.
"The violation in the case of Russia goes further. There is deliberate obfuscation. They have removed IDs. Putin has says he does not know who they are and that anyone can buy military gear in surplus stores.
"It is a deliberate fuzzying of the identification and that is a violation. These troops do not enjoy protection under international law. The Ukrainians would be entitled to shoot them on sight or arrest them as they would any bank robbers. It shows a wanton disregard by Russia for international law.
"A further point. The artillery pieces have had all ID taken away. There are lorries driving around without licence plates.
"What purpose does this game fulfill? They are clearly trained, clearly commanded, doing regular shifts. These are not spontaneous guerrilla groups.
"Special forces can hide ID for a single operation but the military cannot do this for extended periods.
"It shows they have been planning this for a lengthy period or time. It is not just the removal of the ID but the fact they knew where they were being deployed.
"I am surprised the International Committee of the Red Cross has not commented on this. Tthe ICRC is responsible for the much of the current law on warfare, all based on the assumption of a fundamental difference between combatants and non-combatants".
David-Pierre Marquet, a spokesman for the Geneva-based International Committee of the Red Cross, said: "The situation is not so clear." According to the Geneva conventions, all armies should wear their distinctive uniforms. But in the Ukraine, there are lots of different armed groups. "It is difficult to tell about a violation of the convention," Marquet said.
"It is a huge political and diplomatic crisis but in terms of the law, it is not clear."
Marquet added: "In the ICRC, we focus on humanitarian need, not to criticise or judge, not to say who is right or wrong. There are different parties. We are very sensitive to this."
Responsibility of implementing Geneva conventions rests with governments, he said..
In a commentary on the ICRC website dealing with uniforms, Tony Pfanner, editor-in-chief of the International Review of the Red Cross, writes that the military uniform, which came into general use with the appearance of large national armies in the 17th century, had a primary function of identification.
He argues that it is a misinterpretation of the Geneva conventions to deny prisoner-of-war status on the basis that combatants of a regular force failed to wear a uniform. But individual members of regular armed forces can possibly violate the requirement of distinction from the civilian population when not wearing a uniform.
"For the sake of the protection of the civilian population, the military uniform can and should play an important part in meeting the requirement of distinction," Pfanner writes.
Brigadier Ben Barry, a land army specialist at the London-based International Institute for Strategic Studies, said: "It is quite clear. The evidence is overwhelming. These are Russian troops. Some have identified themselves as Russian marines from Sevastopol, all are wearing standard Russian uniforms and although number places have beenb blanked out, some of them have lost their covers and are clearly Russian armed forces number plates.
"There is no requirement about details of uniforms. It simply says you have to fight in uniform. Wearing someone else's uniform is perfidy…..I do not believe wearing the national flag is a mandatory provision of the Geneva conventions," Barry said.
Barry said that another point is that there has not been any fighting in the Crimea so it falls short of a conflict. "It is not a state of armed conflict.," he said.