By Marc Frank

HAVANA (Reuters) - Cuba's Communist government is filtering mobile phone text messages for key words such as "democracy" and "human rights" and then blocking them, dissidents said on Monday.

An investigative report by blogger Yoani Sanchez and journalist Reinaldo Escobar concluded that text messages failed to reach their destinations if they contained Spanish words for democracy, human rights or hunger strike, among others, as well as the names of some dissidents.

Eliecer Avila, head of opposition youth group Somos Mas, which participated in the investigation, said 30 key words that triggered the blocking had been identified but there could be more.

"We always thought texts were vanishing because the provider is so incompetent, then we decided to check using words that bothered the government," he said.

"We discovered not just us but the entire country is being censored," he said. "It just shows how insecure and paranoid the government is."

It was not clear for how long the filter had been in place.

The full report was published by Sanchez's online newspaper,

State telecommunications monopoly ETECSA could not be reached for comment.

Cuba has repeatedly charged that the United States wants to use telecommunications to subvert the government and brands Sanchez and other opponents as mercenaries working with Washington.

Reuters on Monday unsuccessfully tried to send messages containing the words "democracy," "human rights," "Somos Mas" and Yoani Sanchez. Other messages containing the Spanish word for "protest" went through. The messages that did not reach their destinations appeared as "sent" on the users' telephone.

Cuba arrived late to modern telecommunications, authorizing mobile phones in 2008 and Wi-Fi internet access only last year. Online, it blocks dissident websites and media it believes to be funded by the United States, but permits the websites of critical newspapers such as El Nuevo Herald and El Pais.

There currently are about 3 million mobile telephone accounts with local provider CubaCell, which is part of ETECSA.

Despite efforts by the Obama administration to link U.S. internet providers with the country as part of a detente begun in December 2014, Cuban authorities appear more interested in working with Russia on cyber-security, while China provides most of the Caribbean island’s communications technology.

Experts estimate that between 25 percent and 30 percent of Cuba’s 11.2 million residents has some Internet access, mainly through Wi-Fi, though it is sparsely used because of high rates.

Some 5 percent of the population enjoys home-based Internet, which requires special government permission.

(Editing by Frank Jack Daniel; Editing by Bill Trott)