Serbia, Balkans (CNN)- As if the deadly flooding inundating much of the Balkans wasn't alarming enough, rescuers must now grapple with another concern: the risk of land mines buried during the Bosnian war resurfacing.

"A vast number of landslides have worsened the situation and relief efforts," the Red Cross said, describing the rains as the "worst floods in more than a century."

"There are reports that land mines buried during the conflict and not yet removed are in some instances being shifted with the landslides, adding (to) the dangers of people living in the areas as well as rescuers," the Red Cross said.

In Serbia alone, more than 24,000 people have evacuated to escape water that is chest-high in some areas. But many won't budge.

"Some people simply do not want to leave their homes," said Novica Biorac, a volunteer from a rafting club in Raska, said.

"We are trying to convince them to leave, but it's very difficult."

The situation has turned deadly.

At least 12 bodies have been found in the town of Obrenovac, about 35 kilometers (23 miles) from the capital of Belgrade, the Serbian government said Sunday night.

But one of the 12 was someone who had already died "of natural causes," Serbian Prime Minister Aleksandar Vucic said.

One of the deceased was a rescuer, said Dragan Radovanovic, president of the Serbian branch of the Red Cross.

Authorities estimate that 90 percent of Obrenovac has been flooded.

Serbia's not alone. In nearby Bosnia and Herzegovina, at least 13 people have died, Deputy Minister of Security Samir Agic said.

The catastrophic weather has prompted authorities to declare a state of emergency in Bosnia and Herzegovina.

Bosnian authorities say the flooded town of Maglaj received the average rainfall for two months in less than two days.

The epic flooding is the worst Serbia has seen since the country began keeping records 120 years ago, meteorologists said.

"Many cities and villages in western Serbia are completely under water," the Serbian Embassy in Washington said in a statement Sunday, describing the situation as an "unimaginable catastrophe."

Volunteers, soldiers and rescue workers have stacked sandbags in towns near rivers throughout the country, the statement said.

The Prime Minister pointed out that a dam 7.3 meters tall (24 feet) has been erected, but that the current level of the Sava River is over 6.3 meters — a historic high. The river is expected to rise near Belgrade.

He warned that it is difficult to predict what will happen if the river reaches 6.8 meters, or slightly more than 22 feet.

In Kostolac, along the Danube River, workers were building sandbag walls to protect the thermal power plant there — one that the energy minister called the most important power facility in Serbia.

A written statement said it produces 20 percent of the nation's power.

The Prime Minister thanked the many countries that have already come to Serbia's aid.

He was especially grateful to members of the Russian special forces, highlighting one member who swam 200 meters (656 feet) in cold water to save several people.

Russia and Israel each announced Sunday they would send relief supplies.

According to Finance Minister Dusan Vujovic, more than 10,000 troops have already been involved in rescue and assistance operations.

BBN/SS/AS-19May14-1:00pm (BST)