Hugo Chávez's government has been accused of spying on his defeated presidential rival in the runup to the Venezuelan elections, with leaked documents allegedly showing that secret service agents tracked the movements of Henrique Capriles and his family.

Argentinian journalist Jorge Lanata, who said he was interrogated by secret service agents at Caracas airport last week as he left Venezuela, was due to release the files on television on Sunday night. The documents have not been authenticated but are said to come from secret service files.

One report, dated 3 October, is titled Arrival of relatives of MUD presidential candidate Henrique Capriles Radonski, and tracks the arrival of the candidate's aunt, Andrea Radonski, and nine others at La Chinita airport.

Another, marked Secret, states that "with regard to the monitoring under way of the main personalities from the national political arena passing through the International Airport Simón Bolívar de Maiquetía, it is observed that presidential candidate Henrique Capriles Radonski, has not made any trips since 6 August 2012, when he arrived from Maracaibo on board airship 215T".

Others documents report on the infiltration of student groups and he movement of foreign journalists covering last Sunday's polls.

Lanata said secret service agents questioned him for two hours in the basement of Caracas airport, and deleted data from his team's computers, cellphones and cameras before allowing them to leave the country. "They wanted to know where we had got the documents from," said Lanata, who was to reveal their contents on his news programme Periodismo Para Todos (Journalism for All).

Last week, Lanata released documents apparently showing how he and his team were being tracked by the secret service during their stay in Venezuela.

"They kept on asking me for my email password because they wanted to see what other documents I had," said Nicolás Wiñazki, a journalist on Lanata's team. "They thought they had found it when they found my scribbled password for the WiFi at my hotel."

Wiñazki refused to give the agents his password and after nearly two hours in the basement of Maiquetía international airport, he and the rest of Lanata's team were returned their passports, as well as their now emptied cellphones, cameras and computers, and allowed to board their plane to Buenos Aires.

Lanata says he is convinced the documents are genuine because of the interrogation. "The SEBIN (secret service) agents kept asking how we got hold of the documents that we had already aired, so those were definitely authentic. These ones about Capriles came from the same source."

Lanata, a critic of the Chávez government and his ally, Argentina's president Cristina Fernández de Kirchner, expects a strong reaction to his broadcast. "They could charge me with violating Venezuelan secrecy laws. I suppose they could bar me from ever returning to Venezuela or ask for my extradition from Argentina, that would be a great story too."