A Russian fighter jet came ‘‘within several feet’’ of an Air Force RC-135 reconnaissance plane over the Baltic Sea and lingered by the side of the US plane for several minutes on Monday, US military officials said.

The incident comes amid increased tensions between Russian and the United States following the shoot-down Sunday of a Syrian fighter jet by a US Navy Super Hornet after the Syrians bombed US-backed fighters in northern Syria. Russia, which is aligned with the Syrian government and is carrying out military operations in Syria alongside it, condemned the incident and said Monday that it would track US aircraft over Syria.

The Russian Su-27 maneuvered its wingtip within a few feet of the larger, slower RC-135 for several minutes, said Meghan Henderson, a spokeswoman for US European Command. The Pentagon considered the incident, known as an ‘‘intercept,’’ unsafe because of the ‘‘high rate of closure speed’’ and the ‘‘poor control of the aircraft’’ that the Russian pilot had, said Henderson.

The RC-135 is a modified C-135 plane that carries advance sensors that allow those inside to detect and make sense of electronic signals. Its crew typically includes more than 30 people, including electronic warfare officers and intelligence operations and maintenance technicians, according to the Air Force.

The Su-27 is a Russian-made jet that was designed to be competitive with so-called ‘‘fourth-generation’’ aircraft used by the Pentagon, such as the F-16 Fighting Falcon and the F/A-18 Hornet.