the Islamic State jihadist group, a monitor said.
The Syrian Observatory for Human Rights said the blast in the city of Qamishli killed 10 members of the Kurdish forces, called the Asayish, and six civilians.
"A suicide bomber in a vehicle targeted the Asayish's local headquarters in Qamishli," said Rami Abdel Rahman, head of the British-based Observatory.
IS claimed the attack in an online statement, saying a suicide bomber had used a "water tanker rigged with explosives to infiltrate an Asayish command base".
Syrian Kurdish militia have been some of the most successful forces fighting IS in northern parts of the country.
The jihadist group has targeted Qamishli and other Kurdish bastions with suicide operations in the past.
Abdel Rahman described Wednesday's explosion as "massive" and said at least 14 civilians had been wounded.The charred wreckage of several vehicles was seen at the site of the blast in the industrial district of Qamishli, a majority-Kurdish city in Syria's northeastern province of Hasakeh.
Syria's state news agency SANA said 15 people were killed but did not specify whether they included civilians. It said 50 people were wounded.
Arin Shekhmos, a local journalist in Qamishli, said the blast could be heard throughout the city.
"I wasn't close, but I could hear it from where I was," Shekhmos told AFP by telephone shortly after visiting the blast site.
"There is a lot of destruction -- the buildings on at least two streets have been completely destroyed," he said.
Qamishli, under the shared control of Kurdish authorities and the Syrian regime, has been targeted by several bomb attacks this year. In late July, bombs struck the Kurdish People's Protection Units (YPG) and the Asayish, wounding at least three people.
Syria's conflict, which began in March 2011, evolved from peaceful demonstrations to a multi-front war involving Kurds, rebels, jihadists and the regime.
Both pro-regime and opposition forces have been criticised by human rights groups for indiscriminate attacks that have killed civilians.
On Wednesday, aerial bombardment by the government of a rebel stronghold east of Damascus left at least 10 people dead, the Observatory said.
The attacks on Harasta, in the Eastern Ghouta region, killed members of the town's council, civil defence, and police force, it said.
As the largest rebel bastion near the Syrian capital, Eastern Ghouta is often targeted by government forces. On Sunday, nearly 100 people were killed in regime air strikes on the town of Douma.