WASHINGTON (AFP) - The United States on Wednesday denounced an attack on Tunisia's national museum that killed 17 foreign tourists, and vowed to stand with the Tunisian people.

"The United States condemns in the strongest possible terms today's deadly terrorist attack at the National Bardo Museum in Tunis," Secretary of State John Kerry said in a statement.

Extending America's sympathies to the victims and their families, Kerry said Washington "stands with the Tunisian people at this difficult time and continues to support the Tunisian government's efforts to advance a secure, prosperous, and democratic Tunisia."

He also commended the "Tunisian authorities' rapid response to today's wanton violence and their efforts to resolve the hostage situation and restore calm."

Kerry said 19 people had died and 20 were wounded, but Tunisian authorities said that Kalashnikov-wielding gunmen killed at least 17 foreign tourists before dying in a police assault.

Polish, Italian, German and Spanish tourists were among the dead, Tunisian Prime Minister Habib Essid said, adding that two gunmen had been killed.

Kerry often refers to the Tunisian fruit seller whose self-immolation in 2011 set off a series of uprisings and sparked the Arab Spring revolution.

The top US diplomat made a brief, unannounced trip to Tunisia on Tuesday to back the transition to democracy in the North African country in February 2014.