Venezuelan Vice-President Nicolas Maduro is heading a meeting of political and military leaders as concern mounts over President Hugo Chavez's health, state media says. On Monday officials said he had a new, severe respiratory infection. Dozens of people gathered to pray for Mr Chavez's health at the hospital where he is being treated. Mr Chavez, 58, returned to Venezuela last month after being treated for cancer in Cuba. The defence minister and the president's brother Adan Chavez were reportedly among those at the meeting chaired by Vice-President Nicolas Maduro at the presidential Miraflores Palace. The meeting is being broadcast live on state TV. Mr Maduro accused "enemies of the fatherland" in Venezuela and abroad, particularly the United States, of seeking to undermine democracy in Venezuela. He went on to say that Mr Chavez's illness was an "attack" by his enemies and called for this to be investigated. Mr Chavez has not appeared in public since his return from Cuba. In recent days, the opposition have condemned what they say is the lack of clarity surrounding his condition. "The lack of precise information worries Venezuelans and fuels rumours," said Ramon Guillermo Aveledo of the opposition Democratic Unity coalition. At the weekend, hundreds of Venezuelan students and opposition members marched in Caracas demanding full details about Mr Chavez's health. Information Minister Ernesto Villegas accused Mr Chavez's opponents of showing "the same hatred that they have shown towards Chavez all these years. "It annoys them that he won't give up and neither will the people!," he wrote on his Twitter account. On Monday Mr Villegas announced from the military hospital where Mr Chavez is being treated that he had suffered "a worsening of respiratory function" and that his condition continued to be "very delicate". He said Mr Chavez was undergoing "intensive chemotherapy, as well as complementary treatments". "The commander-president remains clinging to Christ and to life, conscious of the difficulties that he is facing, and complying strictly with the programme designed by his medical team," Mr Villegas said. Mr Chavez, who has been in office for 14 years, is believed to have cancer in his pelvic area, but his exact illness has never been disclosed. He announced in June 2011 that he had cancer and has undergone four operations since then, as well as chemotherapy and radiation therapy. The president was re-elected for another six-year term in October 2012, but the Supreme Court ruled that his swearing-in on 10 January could be delayed because of his illness. He is said to be taking decisions about the country from the hospital bed but there have been mixed messages from officials on his condition.