By Daniel Trotta

HAVANA (Reuters) - Politically motivated arrests in Cuba topped 1,000 for a third straight month in February as the result of wider public demonstrations against the one-party state, a leading human rights organization said on Monday.

The Cuban Commission for Human Rights and National Reconciliation said arrests in the past three months have nearly doubled from the monthly averages of the previous two years.

The commission reported 1,051 arrests in February that it considered arbitrary and politically motivated, although all the people jailed were released, usually within a few hours.

The February number was similar to the 1,052 reported in January and down from 1,123 in December.

Reuters could not independently verify the numbers, which the commission's president, Elizardo Sanchez, said were based on first-hand reports from activists around the island. The commission excludes any arrest report that it cannot verify, Sanchez said.

The Cuban government says the commission is illegal and counterrevolutionary, and normally does not respond to its monthly reports.

It generally considers dissident groups to be in the pay of the United States as part of the 55 years of hostility between the two countries since Fidel Castro came to power in a 1959 revolution.

A Reuters request for government comment was not immediately answered on Monday.

The commission said the December number was the highest on record since March 2012, when Pope Benedict visited Cuba. It has been keeping records since 2010, and says the arrests rise when there are international events in Cuba, such as a summit of Latin American and Caribbean leaders in late January.

The numbers have stayed high largely because a growing number of citizens now publicly oppose the communist government, Sanchez said.

The report details each case by name, date and reason for the arrest, with many detentions coming before, during or after organizing meetings or public protests. Other dissenters were held on their way to or from church, the report said.

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"There are more demonstrations of the people's discontent," Sanchez said in telephone interview from Spain, where he is meeting with human rights activists from Cuba and other countries.

Human rights groups say Cuba in recent years has avoided jailing dissidents for lengthy periods, instead choosing to detain them for several hours or days.

As a result, estimates of the number of political prisoners are in the single digits, compared with numbers in the thousands decades ago. Amnesty International reported seven new prisoners of conscience in 2013, of whom three were released without charge.

(Reporting by Daniel Trotta; Editing by Kieran Murray and Andre Grenon)