Police spokeswoman Andrea Zoulova said an explosive - which may have been part of a security mechanism - went off after the safe was opened. "With the greatest probability, an explosive device placed on the door of the safe was triggered," she said.
The Palestinian foreign ministry, in a statement reported by the official WAFA news agency, said the blast happened minutes after Jamal opened a safe that had come from the embassy's old offices.
Some safes can be fitted with small charges to destroy secret documents in the event of the lock being tampered with.
Czech Prime Minister Petr Necas pledged 300 million Czech crowns ($15 million) to relief efforts and said another 2,000 troops were ready to support the 300 soldiers already helping to erect temporary barriers and pile sandbags in Prague and other areas.
"The government approved the declaration of a state of emergency, which will enable a more effective rescue effort," said Necas after an emergency cabinet meeting, adding that there was another 1.3 billion crowns available to help fund the cleanup operation.
The historic area of Prague is a UNESCO heritage site boasting hundreds of well-preserved buildings, churches and monuments dating back centuries, including the Charles Bridge straddling the Vltava that was closed due to high water
Czech Prime Minister Petr Necas declared a state of emergency for most of the nation on Sunday as swollen rivers caused by days of heavy rain threatened Prague's historic centre and forced evacuations from low-lying areas.
Prague authorities limited public transport and planned to close underground stations in the centre of the city as water from the Vltava River overflowed into picturesque areas popular with tourists
The main train line connecting the capital and the east of the country was also shut.