BOGOTA, June 21 (Reuters) - Reported deaths from COVID-19 in Colombia passed 100,000 on Monday, the country's health ministry said, amid warnings of potential scarcity of treatment drugs and oxygen in hospitals during a long and brutal third peak of infections and deaths.

The country of 50 million people has reported more than 3.9 million cases of coronavirus infections, as well as 100,582 deaths.

Colombia has seen record numbers of coronavirus infections and deaths in recent weeks, with some medical officials warning certain medical supplies are running low.

Intensive care units (ICUs) in major cities are operating at near full capacity, according to information published by local health authorities in capital Bogota, as well as in Medellin and Cali, Colombia's second-largest and third-largest cities respectively.

"We're starting to see scarcity of certain resources everywhere," Cesar Enciso, medical coordinator for intensive care at the University Children's Hospital of San Jose in Bogota, told Reuters, citing a lack of sedatives and oxygen supplies.

"If the situation continues with this number of cases every day, resources are going to run out," he added.

The government has blamed weeks of anti-government protests for extending the third peak, which began after Easter. The country hit a record of 30,000 daily reported cases earlier this month, while Monday saw a new high of 648 daily deaths.

"Crowds are the main breeding ground for this disease to spread exponentially," President Ivan Duque said in a ceremony to mark Colombia's COVID-19 deaths.

Despite the peak, the South American country has lifted many of the restrictions it imposed in March last year to control coronavirus, in a bid to bolster the economy and amid widespread frustration with social distancing measures.

Colombia has administered over 14.9 million vaccine doses, of which more than 4.7 million are second doses. The country hopes to vaccinate some 35 million people - 70% of its population - this year.