Armenia and Azerbaijan have been able to agree on the basic principles for a peace treaty but are still "speaking different diplomatic languages", Armenian Prime Minister Nikol Pashinyan said on Saturday, according to Russia's TASS news agency.

The two countries have been at odds for decades, most notably over the breakaway Azerbaijani region of Nagorno-Karabakh, which Baku's forces recaptured in September, prompting a mass exodus of ethnic Armenians from it.

But Pashinyan said there had been some progress in talks over a peace treaty even though he was cited as saying that the two countries still often struggled to agree on some things.

"We have good and bad news about the Armenia-Azerbaijan peace process," TASS quoted Pashinyan as saying in Yerevan.

"It is good that the basic principles of peace with Azerbaijan have been agreed.

"This happened through the mediation of the head of the European Council Charles Michel as a result of my meetings with Azerbaijan's president in Brussels," Pashinyan said.

"The most important bad news is that we still speak different diplomatic languages and very often do not understand each other," Pashinyan said.

Pashinyan said Armenia had also proposed swapping all Armenian prisoners for all Azerbaijani prisoners, TASS reported.

Reporting by Alexander Marrow Editing by Andrew Osborn