US Secretary of State Hillary Clinton is visiting Armenia at the start of a tour of the South Caucusus.
Her trip comes as a ceasefire between Armenia and Azerbaijan is looking increasingly fragile.
The two former Soviet republics fought a bloody war over the disputed region of Nagorno-Karabakh in the 1990s.
The BBC’s Damien McGuinness, in neighbouring Georgia, says it is hoped Mrs Clinton will ease tensions between the two countries.
The region is dependent on US aid so Washington has much influence there, he says.
The conflict between Armenia and Azerbaijan erupted as the Soviet Union collapsed and at least 30,000 people were killed by the time a ceasefire was declared in 1994.
Since then, a simmering stalemate has prevailed and both sides have reported sporadic breaches of the truce.
Both sides have been building up arms in recent months and refusing to compromise.
It is hoped Mrs Clinton will at least call on both governments to tone down the rhetoric and hold peace talks.
Human rights groups also want Mrs Clinton to address alleged abuses in the region.
Azerbaijan’s harsh treatment of government critics has been in the spotlight since it hosted the Eurovision Song Contest in May.
Authorities have dismissed criticism in the international press as Armenian propaganda.
However, condemnation from the US Secretary of State will carry more weight, our correspondent adds.
Mrs Clinton travels on to Georgia on Tuesday and Azerbaijan on Wednesday.