Clare Nuttall in Almaty -

Eight soldiers were shot dead in clashes on the border between Armenia and Azerbaijan on June 4 and 5. The worst outbreak of violence between the two countries for years has raised fears of another escalation in the conflict between the pair.

Three Armenian soldiers were killed and several soldiers from both countries injured in a shootout on June 4, which Armenia's Defence Ministry said was caused by an "invading" group from Azerbaijan. The shootings, happened during US Secretary of State Hillary Clinton's visit to the volatile South Caucaus region.

The following day, five Azeri soldiers were killed in two separate incidents. A statement from Azerbaijan's Ministry of Defence said that a group of Armenian "saboteurs" tried to "infiltrate a position of the Azeri armed forces" early on June 5, and four Azeri soldiers died in the ensuing battle. A fifth soldier died in a nearby skirmish later in the day. On the evening of June 5, Armenian news portal News.am quoted the head of the village of Movses near the border as saying that shooting had continued through the day.

Despite the signing of a ceasefire agreement in May 1994, Armenia and Azerbaijan have never signed a peace settlement to end the war that broke out in the early 1990s over Nagorno-Karabakh. The tiny republic, which was part of the Soviet republic of Azerbaijan but had a mainly ethnic Armenian population, declared its independence in 1991. When Baku tried to regain control by force, Azeri forces were driven out by Karabakhis supported by the Armenian army.

However, the shootings on June 4 and 5 took place on the border between Armenia proper and Azerbaijan, rather than on the de facto border dividing Azerbaijan from Nagorno-Karabakh, which has seen numerous clashes in the last 15 years. A total of 63 people have been killed in skirmishes between Armenia and Azerbaijan since the beginning of 2011.

The latest incidents are, however, the deadliest for several years. There are growing concerns that rather than being isolated incidents, the clashes could escalate into a full-scale war between Armenia and Azerbaijan.

Speaking in Yerevan on June 4, after the deaths of the three Armenian soldiers, Clinton said that there was a risk that violence could lead to a "broader conflict" in the region. "I am very concerned about the danger of escalation of tensions and the senseless deaths of young soldiers and innocent civilians. The use of force will not resolve the Nagorno-Karabakh conflict, and therefore force must not be used," Clinton told journalists at a joint briefing with Armenian Foreign Minister Eduard Nalbandian.

The situation looks eerily familiar. Another frozen conflict in the South Caucasus escalated into full-scale war in August 2008, following a similar series of incidents on the border between Georgia and the self-declared republic of South Ossetia in the first half of 2008. A five-day war promptly erupted between Georgia and Russia, which has consistently supported the breakaway republic.

The clashes appear to cap for now efforts by the international community to bring about a peace settlement between Armenia and Azerbaijan. The push had looked to be progressing in recent years following the election of new presidents in both countries. Azerbaijan's Ilham Aliyev and Serzh Sargsyan in Armenia have both been more amenable than their predecessors to negotiations, and a series of meetings have taken place between the two heads of state - for the first time since 1994 - under the aegis of Russia's now-former President Dmitry Medvedev.

However, the initial optimism that the regular meetings would lead to a breakthrough has faded. Warlike rhetoric has continued in both Baku and Yerevan, and military spending has continued to boost year-by-year (although oil-rich Azerbaijan has considerably out-spent its neighbour). While Nagorno-Karabakh is now de facto independent and closely integrated with Armenia, under international law it remains part of Azerbaijan, and Baku shows no sign of giving up its claim on the territory.