Barack Obama has elevated Tunisia to new allied status, promising financial and security assistance to ensure the North African country's transition to democracy remains a success.
Obama announced in an Oval Office meeting with newly elected Tunisian President Beji Caid Essebsi on Thursday that he intends to designate his country as a major non-NATO ally of the US.
The special status has been granted to only a few countries.
"The United States believes in Tunisia, is invested in its success and will work as a steady partner for years to come," Obama said.
The move recognises the country's democratic progress following its 2011 Arab Spring uprising.
Status as a non-NATO ally qualifies a country for certain privileges supporting defence and security cooperation but does not provide any security commitment to that country.
Other countries with the designation include Afghanistan, Argentina, Australia, Bahrain, Egypt, Israel, Japan, Jordan, Kuwait, Morocco, New Zealand, Pakistan, the Philippines, Thailand and Korea.
The White House has been discussing expanding the designation to other Arab allies.
Essebsi said Tunisia is still midway in its reforms and has a long road ahead, with threats coming from terrorists, anti-democracy forces and an unstable regional environment.
"We need the support of the US, and maybe the US needs Tunisia now," said Essebsi, who was elected in December.
Obama said it was important that the US and Tunisia became partners in counterterrorism and tried to stabilise Libya, which is divided between two rival governments in turmoil, enabling the rise of Libya's Islamic State in Iraq and the Levant (ISIL) branch.
Obama said the goal for Libya is that "we don't have a failed state, a power vacuum that ends up affecting the situation in Tunisia".
ISIL claimed responsibility for a March terrorist attack at Tunisia's Bardo National Museum that killed 22 people, mostly foreign tourists.
Tunisians ended decades of one-man rule in 2011, overthrowing their longtime president, Zine El Abidine Ben Ali, after a street vendor, Mohamed Bouazizi, set himself ablaze after police confiscated his merchandise.
Obama praised Tunisia for inspiring a series of pro-democracy uprisings that became known as the Arab Spring and praised the country's progress since then in incorporating all parties, including women and minorities, in the governing process.
"It bodes well for Tunisia's future and the future of its children," he said.
Obama this year asked the US Congress for at least $100m in assistance for Tunisia, which would bring total support since the 2011 revolution to nearly $700m.
Obama said he would expand economic assistance so ordinary Tunisians could feel the benefits of the change.