TEHRAN — Iranians spent the night digging through rubble in a frantic search for survivors after a powerful earthquake struck near the Iraqi border on Sunday evening, killing more than 300 people and injuring thousands of others, officials said.

The epicenter of the quake was near Ezgeleh, Iran, about 135 miles northeast of Baghdad, and had a preliminary magnitude of 7.3, according to the United States Geological Survey.

Photographs from the region — a patchwork of farms and home to many Kurds, a large ethnic minority in Iran — posted on the internet showed collapsed buildings, cars destroyed by rubble and people sleeping in the streets in fear of aftershocks.

At least 341 people were killed and nearly 6,000 people in Iran were injured, according to the state news agency IRNA, and hundreds of people waited in line to donate blood in Tehran in response to a call from the government.

At least eight people were killed on the Iraqi side of the border, according to Dr. Saif al-Badir, a spokesman for the Health Ministry, and at least 535 were hurt.

Particularly hard hit was Sarpol-e Zahab, a city in the western Iranian province of Kermanshah, according to the semiofficial Iranian Students News Agency. The authorities said that at least 236 people had died in the city, which has a population of 30,000, and the main hospital was believed to be at least partly running.

“My friend was screaming, saying, ‘I lost my home,’ ” one resident wrote on Twitter. “Thank God, she and her family are doing well. She said people were only mourning and their loved ones were under the rubble.”

One image from Sarpol-e Zahab appeared to show the near-destruction of an apartment block recently built for low-income families. Another, posted on the website Khabar Online, showed a pickup truck transporting victims under colorful blankets.

Ayatollah Ali Khamenei, Iran’s supreme leader, delivered a message of condolence on Monday, urging rescue workers to keep searching for survivors. “The officials should hasten in these first hours with all their might and determination to help the injured, especially those trapped under the rubble,” his office reported.

Farhad Tarji, a member of Parliament for Sarpol-e Zahab, told the semiofficial news agency ILNA that his family had been hit hard by the quake. “I’ve lost 15 people,” he said.

The Iranian government newspaper posted a video on its website in which a resident of Sarpol-e Zahab complained that no help had come.

“There has been no help yet, neither food nor water, no clothing, no tents, there is nothing,” said the resident, a man who appeared to be in his 30s, while standing in a street with collapsed buildings. “There are no facilities yet. We’ve slept outside since last night. This is the condition of our homes. Our electricity, water, gas, phone lines are out, everything is completely out, the whole city has been destroyed, it is wrecked.”

An image posted on social media showed soldiers searching through the rubble at night without flashlights or torches, using their cellphones for light.

Officials from the Health Ministry traveled to the area, as did the commander-in-chief of the Islamic Revolutionary Guards Corps, Brig. Gen. Mohammed Ali Jafari, but foreign reporters were not allowed to visit the scene, in a change from previous disasters.

The movement of foreign correspondents is restricted in Iran — travel outside the capital requires a permit from the Ministry of Islamic Guidance and Culture — and reporters from abroad were not given clearance to travel to the quake-hit region.

Initial reports from the Kurdish region of Iraq indicated less damage and fewer deaths on that side of the border. In Sulaimaniya, the second-largest city in Iraq’s Kurdish region, residents described feeling heavy tremors but said there was no notable building damage. Residents in the oil-rich town of Kirkuk, roughly 50 miles to the west, reported similar damage.

The earthquake was felt as far as the Mediterranean coast of Israel. Shiite pilgrims in the Iraqi city of Karbala, for the annual religious commemoration of Arba’een, posted videos of people gathering on the streets after the earthquake.

Iran lies on dozens of fault lines and is prone to quakes. In 2012, a double earthquake in the north of the country killed 300 people. When residents learned of the government’s lackluster relief efforts, some started organizing aid groups themselves. After that quake, the United States, which does not maintain normal diplomatic relations with Iran, sent several planeloads of aid.

In 2003, more than 20,000 people were killed and an ancient citadel was destroyed by a quake that struck the southern city of Bam.

Follow Thomas Erdbrink on Twitter: @ThomasErdbrink.

Falih Hassan contributed reporting from Baghdad.