Ex-Soviet Tajikistan is reinforcing the most most dangerous sections of its border with Afghanistan with more than 1,000 extra troops, military sources told AFP on Friday.

Tajikistan, an impoverished central Asian ally of Moscow, shares a 1,344-kilometer (835-mile) border with Afghanistan, including areas controlled by the Taliban jihadist insurgency.

Tajikistan's parliament on Friday backed changing the constitution to allow the ex-Soviet country's long-serving president Emomali Rakhmon to run for office an infinite number of times.

The 63-year-old president has led the impoverished Central Asian country since 1992.

At least two people were killed and dozens injured when a powerful 7.2-magnitude earthquake struck dangerously close to a high-altitude lake in eastern Tajikistan, authorities in the Central Asian state said Tuesday.

The tremor hit at 7:50 GMT in the ex-Soviet country on Monday, 109 kilometers (67 miles) west of the town of Murghob at a depth of 28 kilometers, the U.S. Geological Survey said.

A powerful 7.2-magnitude earthquake struck eastern  Tajikistan on Monday, U.S. experts said, and state television said one person was killed ten were injured.

The tremor hit at 7:50 GMT in the Central Asian country, some 109 kilometers (67 miles) west of the town of Murghob at a depth of 28 kilometers, the U.S. Geological Survey said.

U.S. Secretary of State John Kerry visited ex-Soviet Tajikistan and Turkmenistan Tuesday to assure their leaders of U.S. support for security on their Afghan borders, as he nears the end of his five-nation tour of Central Asia.

Kerry met veteran Tajik President Emomali Rakhmon at the presidential palace in Dushanbe, pledging U.S. support in the face of instability across the frontier in Afghanistan, but urging the authorities not to use the fight against extremism to crack down on rights at home.

NATO said Wednesday its special forces are supporting Afghan troops in Kunduz after Taliban insurgents seized the city, fought off a counter-attack and advanced on the airport to shore up their biggest victory in 14 years.

Heavy fighting was underway near the northern city's airport where government forces retreated, highlighting the potent challenge the militants pose after their lightning capture of Kunduz.

Afghan troops backed by US air support launched a counter-offensive Tuesday to retake Kunduz, a day after Taliban insurgents overran the strategic northern city in their biggest victory since being ousted from power in 2001.

Gun battles erupted and Humvees rolled in parts of the city as Afghan security forces, who had retreated to the outlying airport after the fall, began a counter-strike backed by reinforcements.

Ex-Soviet Tajikistan's interior ministry said Sunday that four more militants were killed by government forces in a continuation of violence that began with shootouts Friday, and has now left at least 26 dead.

"Government forces of Tajikistan killed four members of a terrorist group during an operation in the Ramit Valley," an MVD spokesperson told AFP of the military operation under way roughly 50 kilometers northeast from the country's capital, Dushanbe. 

Thirteen militants were killed by government forces in Tajikistan on Saturday, with the rebels refusing to surrender, officials said. 

The crackdown followed a day of violence in which nine policemen and another 13 militants were killed in two separate attacks targeting police stations.

Eight police officers were killed and at least five injured in Tajikistan on Friday in two separate shootouts with armed groups that could have been led by rogue law enforcement agents, police told AFP.

An armed group killed four police in an early morning shootout on the outskirts of the capital Dushanbe, a spokesman for the interior ministry told AFP.