MAKHACHKALA, May 12 (RIA Novosti) - A police officer has been shot dead and another injured in a drive-by shooting on a police post in Russia's North Caucasus republic of Daghestan, a source in the republic's foreign ministry said Monday.

The attack occurred late Sunday when militants opened fire with an automatic weapon. A search for the attackers is underway and tighter security measures have been introduced in the region to prevent further attacks.

"So far, none of the attackers have been detained," the source said.

In a separate development, a home-made explosive device equivalent to around 300 grams of TNT was found in the neighboring North Caucasus republic of Ingushetia.

The device a plastic bottle packed with explosives was disarmed after being discovered in a pile of gravel near a street. Police said the bomb would have been detonated by a cell phone.

An investigation is underway.