An unspecified number of servicemen have been injured in an insurgent attack on their camp in eastern Ukraine, the country's border guard service said Monday.

In a statement, officials from the service said some 100 armed insurgents attacked the border guards' camp in Luhansk, a major eastern Ukrainian city not far from the Russian border, in the early hours.

Border guards responded with fire on the attackers whose numbers swelled to 400 a few hours later. The fighting was ongoing, the border guard service said.

Border guards lamented that neither the army nor the police has arrived with reinforcements yet.

For weeks, Russian-speaking eastern Ukraine has been the scene of deadly clashes between government troops and pro-Russian insurgents.

Three months of protests during the winter drove pro-Russia president Viktor Yanukovych to flee the country. Many in Ukraine's east are suspicious of the new pro-Western government in Kiev.

Protesters in the east were rallying in early spring in favor of greater independence from the Ukrainian capital but that soon turned into a separatist movement as the Luhansk and the Donetsk regions declared independence following hastily called referenda.

The conflict between Ukrainian government forces and pro-Russian insurgents in eastern Ukraine escalated markedly in the last week, with rebels attempting to seize a major airport and the shooting down of a Ukrainian military helicopter.