The widespread availability of the potent synthetic painkiller fentanyl helped drive overdose deaths higher during the first half of 2016 in Massachusetts, an indication that the opioid crisis is showing no sign of ebbing despite increasing political and law enforcement focus on the problem.

Massachusetts is one of the few states to report overdose estimates in close to real time, providing an early indicator of what might be happening nationally. The US Drug Enforcement Administration last month labeled fentanyl an “unprecedented threat” and warned the expanding market for the drug “will likely result in more opioid-dependent individuals, overdoses and deaths.”

The number of opioid-related deaths in the first half of 2016 was estimated to be as high as 986 by the Massachusetts Department of Public Health — a 26 percent increase over the first six months of 2015.

Last year was already the deadliest year on record for opioid-related deaths in the state, with 1,531 confirmed deaths for the full year.

In cases where toxicology screens were done on overdose victims in the first six months of this year, fentanyl was detected in two-thirds of the cases, state officials reported. That compares with 57 percent in 2015.

“As this report details, the prevalence of fentanyl increases the lethality of overdoses,” Marylou Sudders, the state’s secretary of health and human services, said in a statement.

Fentanyl, which can be up to 100 times more potent than heroin, has flooded the US market as drug dealers have found it easy to obtain and many times more profitable to sell than other opioids. In addition to being more lethal, fentanyl is often sold on the street as something else to unknowing users.

In Boston, for instance, police warned in June that dealers were selling fentanyl pills made to look like the popular prescription painkiller oxycodone. In other parts of the country, people have died after ingesting fentanyl they thought was heroin or Xanax.

Dealers are also mixing fentanyl with heroin, with deadly results. A type of fentanyl used to sedate elephants, called carfentanil, is suspected of causing nearly 300 overdoses and 23 deaths during the past month in Akron, Ohio.