(Adds US official comments)
By Arshad Mohammed and Patrick Markey
TUNIS, Feb 18 (Reuters) - U.S. Secretary of State John Kerry made an unannounced visit to Tunisia on Tuesday to praise democratic progress in the country where the "Arab Spring" began and discuss its efforts to tackle Islamist militants, his staff said.
After a crisis last year brought on by the killing of two opposition leaders, Tunisia's transition got back on track when it adopted a new constitution last month and ruling Islamists stepped down for a caretaker administration to govern until elections this year.
Kerry's visit was meant to highlight progress made since the 2011 uprising that brought down autocrat Zine el-Abidine Ben Ali and the compromises new Tunisian leaders, unlike their Egyptian and Libyan counterparts, have made, U.S. officials said.
"What's positive and even inspiring in Tunisia is the demonstrated willingness not to take power, and hold on to it, and see it as a zero sum game, but to find some degree of compromise," a senior U.S. official told reporters as Kerry flew to Tunis.
Kerry was also likely address the many challenges facing the North African nation, among them persistent violence by Islamist militants whose leader has pledged allegiance to al Qaeda's North African wing, officials added.
During his meetings with the Tunisian president and prime minister on Tuesday, Kerry plans to urge the government to do more to arrest and prosecute those responsible for a 2012 attack on the U.S. embassy in Tunis, U.S. officials told reporters traveling with him.
Tunisia's security forces have been battling militants from the banned Islamist movement Ansar al-Sharia, one of the hardline militant groups to emerge after Ben Ali's fall.
Ansar al-Sharia was blamed for inciting the storming of the U.S. embassy in Tunis on Sept. 14, 2012 and has since been listed by Washington as a terrorist organisation, with ties to al Qaeda in the Islamic Maghreb.
Kerry's visit to Tunisia is the first by a U.S. secretary of state since that incident, which occurred three days after an attack on a U.S. diplomatic mission in Benghazi in neighboring Libya killed the U.S. ambassador and three other Americans. (Reporting by Arshad Mohammed and Patrick Markey; Editing by John Stonestreet)