Assad said in the interview that neither Syria nor Russia is responsible for an attack on a UN aid convoy and warehouse that killed 12 aid workers near the besieged city of Aleppo on Monday.
His comments came amid reports of more airstrikes on targets in Aleppo. Activists said six people were killed on Thursday and 50 on Wednesday.
Assad blamed the US for the apparent breakdown in the ceasefire. "I believe that the United States is not genuine regarding having a cessation of violence in Syria," he said.
"We announced that we are ready to be committed to any halt of operations, or if you want to call it ceasefire, but it's not about Syria or Russia; it's about the United States and the terrorist groups that have been affiliated to ISIS and al-Nusra and Al Qaeda, and to the United States and to Turkey and to Saudi Arabia," Assad said.
Assad insisted that his regime was not responsible for Monday's raid on the aid convoy and called US accusations
"It has never happened before, so why to happen now, either by the Russians or the Syrians? No, it's a claim."
Assad said he believed the US-led coalition airstrike against a Syrian army base that killed at least 62 soldiers on Saturday was a deliberate act.
"It's not [an accident], because it wasn't an accident by one airplane for once, let's say. It was four airplanes that kept attacking the position of the Syrian troops for nearly one hour, or a little bit more than one hour. You don't commit a mistake for more than one hour," he said.
"ISIS militants attacked right away after the American strike. How could they know that the Americans are going to attack that position in order to gather their militants to attack right away and to capture it one hour after the strike? So it was definitely intentional, not unintentional as they claimed."
Assad also denied that his troops were blocking aid from reaching besieged areas of Aleppo.
"If there's really a siege around the city of Aleppo, people would have been dead by now," he said.
Assad also said he did not believe there could be a joint US-Russian military partnership against militants -- a key plank of the faltering ceasefire agreement.
"The United States doesn't have the will to work against al-Nusra or even ISIS, because they believe that this is a card they can use for their own agenda. If they attack al-Nusra or ISIS, they will lose a very important card regarding the situation in Syria. So, I don't believe the United States will be ready to join Russia in fighting terrorists in Syria," he said.
On the upcoming US election and the possible impact of a new US president on his regime, Assad said that what candidates say during their campaign differs from what they do in office.
Assad said, "As we see now the American officials, they say something in the morning and they do the opposite in the evening. So, you cannot judge those people according to what they say."
On Wednesday, US Secretary of State John Kerry said Syria's future was "hanging by a thread" and called for all war planes over Syria to be grounded. Meanwhile, Russian Foreign Minister Sergey Lavrov said the United States had not done enough to rein in Syrian rebels under its influence.
Since then, fresh reports of casualties have emerged.
At least six people were killed and 16 wounded in airstrikes on Thursday in Aleppo, an Aleppo Media Center activist told CNN. The airstrikes are in addition to artillery and missiles being fired from positions around the front lines of the rebel-held areas, the activist said.
Civil defense workers were trying to pull people from beneath the rubble after two neighbourhoods -- Bustan al-Qasr and Al-Kalasseh -- were hit with incendiary bombs, the activist said.
At least 50 people were killed and a very large number wounded after an intense bombardment of neighborhoods in eastern Aleppo and in the countryside on Wednesday, he said, adding that warplanes and helicopters were flying overhead.