Russian authorities found and defused a bomb in the southern Russian city of Rostov-on-Don on Saturday, foiling what was believed to be an attempted terrorist attack, officials said.
At about 4:45 am (0045 GMT), a cardboard box was discovered outside a police station in Rostov-on-Don, and on further examination it was discovered to contain a bomb, Russia's investigative committee said.
The box contained "a homemade explosive device consisting of a mobile phone, two detonators and incapacitating elements in the form of nails," the committee said in a statement.
A police source told the RIA-Novosti news agency that the explosive device contained a 1.5-litre bottle with an ammonia mix and aluminium powder. The Interfax news agency said it had been found by a policeman on patrol.
The bomb was successfully defused and authorities opened a investigation on charges of terrorism and unlawful preparation and use of explosives, the investigative committee said.
Russia has been on edge about militant attacks ever since a double suicide bombing in the Moscow metro killed 40 people last month.
A radical Islamist group based in Russia's volatile North Caucasus claimed responsibility for the metro bombing.
Rostov-on-Don is in southern Russia about 1,200 kilometres from Moscow but lies outside the North Caucasus, where bombings and attacks on police targets occur regularly.
The city is due to host an EU-Russia summit next month.