BAKU, Sept 20 (Reuters) - Washington called on Azerbaijan to halt the military action it launched into Armenian-controlled Nagorno-Karabakh on Tuesday, while Russia urged both sides in the conflict to stop the bloodshed in the mountainous and disputed region.

After months of rising tensions in the Armenian-controlled Nagorno-Karabakh in the South Caucasus, Azerbaijan sent troops backed by artillery strikes into the region in an attempt to bring the breakaway region to heel.

Karabakh is internationally recognised as Azerbaijani territory, but part of it is run by separatist Armenian authorities who say it is their ancestral homeland.

U.S. Secretary of State Antony Blinken held calls with both Azerbaijani President Ilham Aliyev and Armenia's Prime Minister Nikol Pashinyan, urging Baku to de-escalate the situation.

"I spoke to Azerbaijani President Aliyev today and urged him to immediately cease military actions in Nagorno-Karabakh," Blinken said on social media.

In a readout of the call, the U.S. Department of State said that Aliyev "expressed readiness" to stop hostilities and hold a meeting with representatives of Nagorno-Karabakh.

Blinken told Pashinyan in their call that Armenia has Washington's full support.

Armenia took control of large swathes of territory in a war that unfolded as the Soviet Union collapsed. Azerbaijan took most of it back in a six-week conflict in 2020, ended by a Russian-brokered truce.

It was not clear whether Baku's actions would trigger a full-scale conflict dragging in Armenia, but the fighting in Karabakh could alter the geopolitical balance in the South Caucasus.