(CNN) -- Tension brewed Wednesday between the United Nations and Syrian rebels after about 30 rebels detained 21 U.N. peacekeepers and refused to let them go.
The U.N., in turn, is demanding they be released.
The rebels contend that the peacekeepers entered a Syrian village near the Israeli-occupied Golan Heights, an area where peacekeepers should not be and where intense fighting has been raging for days between rebels and government forces.
The rebels say they suspect the peacekeepers were trying to aid their enemy, which is defending the regime of President Bashar al-Assad.
The United Nations confirmed the peacekeepers' detention and explained that the peacekeepers were on a "regular supply mission." The U.N. offered no further details of that mission but said it is "dispatching a team to assess the situation and attempt a resolution."
There are two videos rebels posted on YouTube that present the rebels' point of view.
In one, a rebel insists that the peacekeepers will be held until al-Assad's forces withdraw from the village of al-Jamlah, where there has been heavy fighting.
"We demand from America, U.N. and the Security Council to intervene and get al-Assad forces to withdraw, then we will release these detainees," the rebels say.
The other video shows rebels walking near several U.N. trucks.
"This U.N. force entered Jamlah village to assist the regime ... and (the U.N. is) claiming that they are here just to stop the clashing," a rebel says.
Members of the U.N. Security Council condemned the detainment and demanded the peacekeepers be released.
The 21 peacekeepers are Filipino, the Philippine government said Thursday.
"The apprehension and illegal detention of the Filipino peacekeepers are gross violations of international law," Foreign Affairs Secretary Albert del Rosario said in a statement.
The peacekeepers are reportedly unharmed, and negotiations are underway to secure their safe release, the Philippine government said. The Department of Foreign Affairs said said it is coordinating efforts with the United Nations' peacekeeping agency.
The rebels posted on Facebook a letter to U.N. Secretary-General Ban Ki-moon and the leaders of the Organization of Islamic Cooperation and the League of Arab States.
"What is happening (is a) genocide for the Syrian people with the world watching and listening (and) will lead to the gravest consequences," they wrote.
"The blood of the people of Syria will be a curse on the whole world if there" is "no effective action," it said.
The letter pointed out that the city of Homs is under constant bombardment.
There has been "hardly a Syrian village spared from the regime bombing" the letter said.
"This might be the last message to you," it warns. "I call on you all to bear your international responsibilities before God and the people."
The letter is signed by Ahmed Moaz al-Khatib, the president of the Syrian National Coalition, an umbrella body of anti-Assad rebels.
Deadly explosion hits rebel city
Violence continued to plague the country this week, as Syria marked the second anniversary of the war. At least 62 people died across the nation Wednesday.
Also on Wednesday, a massive explosion ripped through the city of Raqqa, two days after rebels claim to have captured this provincial capital.
"Honestly, I cried when I saw the bodies. It's the first time I witnessed such ugly images," said Ahmed Tayar, a writer and resident of Raqqa who saw the aftermath of the mysterious blast.
Tayar, 50, told CNN he saw 19 burned bodies at the scene of the blast.
An uncut, six-and-a-half-minute amateur video of the immediate aftermath of the explosion showed panicked rebel fighters and civilians racing to pick up several wounded and apparently dead men.
In the video, two middle-age men lay bleeding in the street next to scattered oranges and tomatoes that they appeared to have been carrying. Smoke billowed in the distance from a burning car. The entire facade of a nearby three-story building appeared to have been blown off by the force of the blast.
It's not clear what caused the explosion, but supporters of the opposition were quick to blame the Syrian government for the blast.
"I thinks it's the regime who killed those people, and that is because the regime wants to take revenge against Raqqa because that it's the first province that was fully liberated," Tayar told CNN.
On Tuesday, eyewitnesses told CNN residents were fleeing rebel-controlled Raqqa, as government war planes bombed targets in the city.
"While we were there, there were two MiG fighter jets running above us that were throwing down missiles," said Ibrahim Olabi, an activist with the Aleppo Media Center, after he visited Raqqa on Tuesday.
"There were no ground clashes," he added, "but only airstrikes from above."
CNN's Hamdi Alkhshali, Richard Roth, Ivan Watson and Elizabeth Joseph contributed to this report.