Nineteen people, including 17 foreign tourists, have been killed after gunmen targeted a museum in the Tunisian capital, the prime minister says.

Italian, Spanish, Polish and German citizens were among those killed, as well as a Tunisian and a police officer, PM Habib Essid said.

Media reports suggest the death toll could be as high as 22.

Security forces killed two gunmen and were searching for accomplices, the prime minister said.

The attack happened at the Bardo Museum in central Tunis.

At the time of the attack deputies in the neighbouring parliamentary building were discussing anti-terrorism legislation. Parliament was evacuated following the attack.

At least 22 tourists and two Tunisians were injured in the attack, Mr Essid said.

Italian, Polish, Spanish, South African, French and Japanese tourists were among the injured, Mosaique FM radio reported.

Mr Essid said: "It is a critical moment in our history, and a defining moment for our future."

"We have not established the identity of the two terrorists... Reports are not final, these two terrorists could have been assisted by two or three other operatives."

Security operations were "still underway", with forces "continuing to comb the area to find out the remaining operatives, if any", he said.

The remaining hostages held at the museum had been freed, Reuters news agency reported, citing an unnamed government official.

Local television footage showed tourists fleeing to safety, escorted by security forces.

A museum employee told Reuters the two attackers "opened fire on the tourists as they were getting off the buses before fleeing into the museum".

'Tanks rolling in'

Eyewitness Yasmine Ryan told the BBC there had been "a growing crowd" of at least 500 people outside the museum following the attack.

She said she saw "helicopters flying overhead" and "tanks rolling in" as the security situation unfolded.

The attack is a huge blow for Tunisia's tourism industry and its government, which only emerged at the end of a long political transition several months ago, the BBC's Arab affairs editor Sebastian Usher reports.

Islamist militants have tried to derail the democratic transition, which, although fragile, remains the most positive result of the Arab Spring in the Middle East, our correspondent adds.

EU foreign policy chief Federica Mogherini offered her condolences (in French) to the victims' families,

"The EU is determined to mobilise all the tools it has to fully support Tunisia in the fight against terrorism," she added.

The Bardo museum, renowned for its collection of antiquities, is a major attraction in Tunis.

Tourism is a key sector of Tunisia's economy, with large numbers of Europeans visiting the country's resorts.

In 2002, 19 people, including 11 German tourists, were killed in a bomb blast at a synagogue in the resort of Djerba. Al-Qaeda said it had carried out that attack.

Concerns about security in Tunisia have increased in recent months as neighbouring Libya has become increasingly unstable.

A large number of Tunisians have also left to fight in Syria and Iraq, triggering worries that returning militants could carry out attacks at home.

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The Bardo National Museum

 Tunisia's largest museum, built in a 15th Century palace
 Contains 8,000 works, including one of the world's largest collections of Roman Mosaics
 Some items in the collection are over 40,000 years old
 A new wing was added in 2009, doubling its size
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(BBC)