More than 1,000 refugees fleeing fighting between the army and leftist guerrillas in Colombia have crossed the border into Ecuador in recent days and a local official warned Saturday that the number could rise.

Aid groups say the refugees are scared and hungry, and relief workers are struggling to provide them with food, mattresses and clothing in shelters in the Ecuadorean town of San Lorenzo, eight miles from the Colombian border.

"We are handing out light clothing, but we lack cooking gear and we have only about 300 of the 600 mattresses we need," said Felipe Basan, disaster relief coordinator for the Ecuadorean Red Cross.

The United Nations said Friday that more than 800 Colombian refugees were staying in shelters in San Lorenzo. But officials in Ecuador said that by Saturday the number had increased to about 1,100.

"We don't know how long they are going to be here and we expect that more people will be arriving," said San Lorenzo Mayor Gustavo Samaniego.

There are currently about 250,000 refugees living in Ecuador, the U.N. said in a statement.

Most of them are Colombians who have fled an internal armed conflict that has raged there for more than 40 years.

The U.N. estimates about 3 million Colombians have been driven from their homes by violence without leaving the country — making it the largest internal refugee population in the world after Sudan. The government's definition of a refugee puts the number at about 2 million.

Vice President Lenin Moreno called on Colombia to resolve the refugee problem.

"It pains us what is happening in our neighboring country, but unfortunately it is not our problem," Moreno said. "It is a problem that they should resolve."

Francisco Ortiz of the Red Fronteriza de Paz, a group representing border communities in Ecuador, said the recent flight was prompted by fighting between Colombia's army and National Liberation Army guerrillas near their communities.

Ortiz said the refugees arrived Thursday "in the worst human condition," and that many were scared, hungry and sick.

Colombian President Alvaro Uribe, however, accused his nation's largest guerrilla group, the Revolutionary Armed Forces of Colombia, of forcing peasants to flee to Ecuador in a bid to undermine relations between the nations.

Officials from the U.N. High Commissioner for Refugees were en route to assess the situation, U.N. spokeswoman Andrea Escalante said Friday.