The government plans to initiate peace talks with Eta for a permanent ceasefire.
Spain suspends dialogue with Basque separatists after airport is bombed.
Terminal Four at Barajas Airport was evacuated after an initial warning was telephoned to motorway rescue services in the Basque Country, state radio reported.
The bomb exploded at about 9am [08:00 GMT], causing minor injuries to four people including two police officers and a taxi driver, emergency services said, and sending a huge pall of smoke over the airport terminal.
Shortly after, a separate caller to emergency services said the bomb had been planted by Eta, a spokesman for the Basque regional government said.