KAMPALA (Reuters) - Uganda’s main opposition leader was arrested and charged with murder, police said on Friday, after they broke up a rally organized to protest moves to extend President Yoweri Museveni’s rule.

FILE PHOTO: Opposition leader Kizza Besigye speaks during a news conference at his home at the outskirts of Kampala, Uganda, February 21, 2016. REUTERS/Goran Tomasevic/File photo

Kizza Besigye, who has contested and lost four elections against long-time leader Museveni, was detained on Thursday.

Police blamed Besigye for the deaths of two protesters during Wednesday’s rally, in which officers fired bullets and teargas during clashes with government opponents.

“Besigye and his colleagues led these youths who stoned police and caused deaths,” police spokesman Denis Namuwoza told Reuters.

Wednesday’s clash in Rukungiri near the Rwandan border was one of several violent anti-Museveni protests that have spread across Uganda since the president last week for the first time openly expressed support for proposed legislation aimed at allowing him to stay in power.

In office for more than three decades, 73-year-old Museveni would be barred from running again in the next election in 2021 by a law that caps the age of presidential candidates at 75.

The proposed legislation would remove that age ceiling.

Besigye, Museveni’s former physician during the guerrilla struggle that brought him to power in 1986, has claimed the four elections the pair contested were all rigged - something Museveni has denied.

The president has been a staunch western ally widely seen as an anchor of stability in East Africa’s often volatile Great Lakes region.

He has deployed troops in Somalia to help fight Islamist group al Shabaab, earnings plaudits from his western backers.

‘HEAVY-HANDED TACTICS’

Besigye was arrested near the Rwandan border on Thursday, along with two other senior officials of his opposition Forum for Democratic Change (FDC).

Police spokesman Namuwoza said they had been charged with murder, assault, inciting violence and unlawful assembly, and transferred to a prison near the capital Kampala.

There was no immediate reaction to the arrests from Uganda’s opposition.

The proposed new law is widely seen by critics as paving the way for Museveni to rule for life. Similar moves in the Democratic Republic of Congo and Burundi have spurred unrest.

Civil society organizations accused of helping rally support against extending Museveni’s rule have had their premises raided, offices searched and equipment confiscated.

Two of them, Great Lakes Institute for Strategic Studies (GLISS), a think tank, and ActionAid, a South Africa-based international charity, have had their bank accounts frozen on police orders.

In a statement on Thursday, the U.S. Embassy in Kampala criticized what it called “heavy-handed tactics of security forces” which it said harmed democracy.

“Government must protect people’s rights of assembly and expression,” it said.