(For all of the latest coverage of this incident, visit this page)

Initially there was little indication it was necessarily more than an isolated criminal incident, but within several hours it had developed into a diplomatic row, with the Estonian and Russian intelligence agencies advancing completely opposite versions of the events.

The report of the abduction broke around 16:00, seven hours after it happened. At about 19:00, the FSB, the Russian security agency, was first to mention the name of the agent, Eston Kohver, which was later confirmed by the ISS. That was the only detail consistent in the versions, with the Russians putting forward a claim that Kohver was captured on the Russian side.

However, Russian border guards said earlier in the day they had no knowledge of the incident. The ISS also said that Russian border guards went to the scene with them and established that there had been a struggle. Nor did the Russian side provide any evidence that Kohver had strayed into Russia.

President Toomas Hendrik Ilves returned from a late meeting at the ISS (KaPo or Kaitsepolitsei in Estonian) at 23:00 and tweeted: "Just back from KAPO. Confirmed that abduction occurred in the course of cross border corruption investigation. Documented. On Estonian soil."

The ISS said the incident occurred at about 9:00 on the Estonian side of the border and was preceded by jamming of communications and use of a smoke grenade; the interference was said to originate from the Russia side.

The ISS said the official was in the process of interdiction of a cross-border crime.

The area is in Võru County, by Russian border post #121. The border lacks major fortifications; the area is thinly populated.

The whereabouts of the official were not known at first. Martin Arpo, deputy director of the ISS, told Delfi later in the evening that he had been told by the Russians that the official was alive and well and in the hands of the FSB, but that he had yet to obtain confirmation.

There was no immediate explanation on the late disclosure of the incident - more than six hours after it occurred - which comes during a period of more tense relations with Russia.

Officials at Press Conference: Bilateral Border Guard Meeting Held; Russians 'Knew Nothing' of Abduction

Officials from the ISS (Kaitsepolitsei or KaPo in Estonian) and the Office of the Prosecutor General held a press conference at 17:00.

Arnold Sinisalu, director general of the ISS (pictured, center), said that Estonian and Russian border guards met for a briefing at the Estonians' initiative at 13:00. At the meeting on the border, the Russian side said it had no reports of the incident. Both sides visited the scene and established that there were indeed signs of a violent struggle with tracks leading to the Russian side, Sinisalu said. Sinisalu added that there was no indication of a firefight, or of an injury or bloodshed.

Asked for other details, such as whether the official was alone, Sinisalu said they were not immediately available or could not be released yet. He did, however, rule out terrorism.

He cautioned against speculation on the identity of the agent. He said he did not want to speculate on the motive and said there was no clear political reason.

A criminal case has been launched on counts of abduction and illegal border crossing.

Foreign Ministry Summons Russian Diplomat

The Ministry of Foreign Affairs sent for Russia's ambassador to Estonia, Yuri Merzlyakov, today to ask for an explanation.

Foreign Minister Urmas Paet said: "This is a very galling incident. We expect full assistance and cooperation from Russia in resolving the incident and bringing the Estonian citizen back to Estonia."

He said the Estonian Embassy in Moscow was in contact with the Russian Foreign Ministry as well.

Head of State and Government Comment

The Estonian president and prime minister issued their separate comments on the situation.

"Our number one task is to do all we can to get the [security] police official released," said Prime Minister Taavi Rõivas in a media statement. "We await all facets of cooperation and legal assistance from Russia." He said the kidnapping of a counterintelligence official was a serious crime that was "unacceptable to any Estonian."

President Toomas Hendrik Ilves's remarks, issued around the same time on Facebook, also expressed these sentiments.

Despite Timing and Charged Overtones, Interior Minister Says No National Security Threat

Interior Minister Hanno Pevkur told uudised.err.ee: "Estonia is secure and protected. This individual case has to be rapidly resolved like any other crime committed on Estonian territory. I am sure that the persons responsible for security in Estonia will resolve the situation quickly."

He said Estonian security personnel were making maximum efforts to find the official and secure his or her release.

The incident comes two days after a visit to Estonia by US President Barack Obama and in the middle of NATO's summit in Wales. Airspace violations have been reported as increasing by even non-allied Finland.

Last Serious Casualty Among ISS Officers Was in 2011

The most recent serious incident involving the Estonian Internal Security Service was in 2011, when officer Tarmo Laul was killed in a firefight, also in otherwise quiet southern Estonia. In that case the ISS was raiding a farm where arms dealers were using buildings as a warehouse. The suspects, one of whom was also killed, had ties to Russia and was involved in cross-border arms trading.