* Troops trying to flush militants out of Chaambi area
* Al Qaeda's north Africa wing has claimed past attacks
* Remote border access with Algeria complicates operation (Adds comments from commander, details on attack)
By Tarek Amara
TUNIS, July 17 (Reuters) - At least 14 Tunisian soldiers were killed when gunmen with rocket-propelled grenades attacked two checkpoints in the remote Chaambi mountains, the deadliest militant strike on the north African country's armed forces.
Since April, thousands of Tunisian soldiers have been deployed to the Chaambi range bordering Algeria in an operation to flush out al Qaeda-linked militants seeking refuge there, some since fleeing French intervention in Mali last year.
Militants ambushed the checkpoints on Wednesday night, killing the soldiers as they were breaking their fast for the evening during the Muslim holy month of Ramadan, the Defence Ministry said. More than 20 soldiers were wounded.
"It was two simultaneous terrorist attacks when they were breaking their fast. Bodies of nine burned after they were hit with an RPG. Five more were shot." said Col. Major Souhail Chmangi, chief of army land forces. "This is open warfare."
Another soldier is missing after the attack, but authorities could not confirm if he had been kidnapped.
Tunisia's stock market dropped 0.33 percent after the news of the deaths.
Tunisia has struggled with the rise of radical Islamist militants since the 2011 popular revolt ended the rule of autocrat Zine el-Abidine Ben Ali and began its fragile steps towards democracy.
Militants calling themselves Okba Ibn Nafaa Brigade claimed responsibility on a social media site. That claim could not be verified, but Tunisia says the group is operating in Chaambi and is tied to al Qaeda's north Africa wing.
Al Qaeda in the Islamic Maghreb, the north Africa branch, has also claimed attacks in Tunisia in the past, but another militant group, Ansar al Sharia, listed as a terrorist organization by Washington, is also active.
The mountain range is tough terrain with access into Algeria allowing small groups of fighters plenty of cover. Tunisian forces conducted several raids there and have bombarded caves after eight soldiers were captured and killed last year.
Algeria's military, experienced in battling its own Islamist militancy, has been coordinating on its side of the frontier, especially with sharing intelligence. But despite their large presence, Tunisian troops have been harried by improvised landmines and the porous border complicates tracking militants who use the area as a training ground.
One of the Arab world's most secular states, Tunisia has taken steps towards democracy since the 2011 revolt. It adopted a new constitution and allowed a caretaker government to take over until elections this year as a way to ease tensions between a leading Islamist party and secular opponents.
But hardline ultra-conservative Islamists are still influential, and Tunisia is one of the main sources of jihadist fighters travelling from north Africa to fight with Islamist groups in Syria and Iraq.
Last year a Tunisian man who had travelled to fight in Syria returned to carry out a suicide attack on a beach resort near the capital, killing only himself, but shocking a country that relies heavily on foreign tourism for revenue.
Tunisian officials also worry about arms and fighters spilling over from neighbouring Libya, where the weak government is unable to impose order on brigades of former rebels and militias still fighting since the 2011 fall of Muammar Gaddafi. (Reporting by Tarek Amara, writing by Patrick Markey; Editing by Janet Lawrence)