A Russian jet flew within 5ft (1.5m) of a US reconnaissance plane’s wing tip over the Baltic Sea on Monday, US officials say.
The encounter was deemed “unsafe” due to the Russian pilot’s “high rate of closure speed and poor control of the aircraft”, officials said.
But Russia disputes this, saying the US plane made a “provocative” move.
Meanwhile, a Russian plane carrying the defence minister was buzzed by a Nato jet, Russian media reports say.
The F-16 fighter jet was chased away by a Russian Su-27 military jet over the Baltic, according to the state-owned news agency Tass, which had a reporter on the plane.
It said minister Sergei Shoigu was en route to the Russian enclave of Kaliningrad, over international waters, but it did not give further details.
The incidents come amid renewed tensions between Washington and Moscow, sparked by the US downing of a Syrian jet after it targeted American-allied rebels.
In response, Russia, an ally of the Syrian government, warned on Monday that US jets flying in Syria would be treated as targets. On Tuesday, the US military shot down an armed Iranian-made drone in Syria.
The first incident over the Baltic, on Monday, occurred 25 miles (40 km) from Kaliningrad, also over international waters.
Pentagon spokesman Captain Jeff Davis told reporters: “We were flying in international airspace and did nothing to provoke this behaviour.”
Inching towards a clash? Jonathan Marcus, BBC defence and diplomatic correspondent
What happened on Monday is only the latest incident in a continuing pattern of near-misses where Russian and Nato aircraft have come into close proximity.
The two sides’ narratives are very different but independent studies have tended to support Nato’s case that more aggressive Russian behaviour is in large part to blame – this a response to Nato’s stepped up military deployments in central Europe in the wake of Russia’s seizure and annexation of Crimea.
These tensions risk accident and injury but are very different to the situation in Syrian air space where the US, its coalition allies and Russian and Syrian warplanes are all engaged in combat sorties.
Unlike in Europe there is a direct link between Russian and US commanders to avoid dangerous incidents – and although Russia is saying that this has been suspended in the wake of the US shooting down of a Syrian jet – the US side insists that the channel remains open.
The US RC-135 reconnaissance aircraft had been flying with its transponder on, making it visible to other aircraft, he added.
But Russia’s defence ministry said it was the US plane that behaved dangerously after it was already intercepted and was being escorted by a Russian Su-27 fighter jet.
“During the escorting, the RC-135 crew made an attempt of closing with the Russian fighter, performing a provocative turnaround toward the Su-27,” the Tass news agency quoted the Russian ministry as saying.
About 10 minutes later, another US surveillance plane arrived, and it too was intercepted by a SU-27 jet, the ministry said.
Earlier this month, the US Air Force deployed 800 troops and long range B-52 bombers to the United Kingdom to take part in joint Nato exercises.
There have been more than 30 interactions between US and Russian planes and ships in the Baltic Sea since the beginning of June, US officials tell CNN.
The majority have been deemed safe, US officials say.