Syria condemned U.S. missile strikes on a Syrian air base in retaliation to a chemical attack on civilians, describing them Friday as a "blatant act of aggression."

The Syrian military said at least six people were killed in the strike. Russian Defense Ministry spokesman Maj. Gen. Igor Konashenkov said six Syrian jets were destroyed but the air base's runway was intact. He said “the combat efficiency of the U.S. strike was very low" and that 23 of the 59 missiles fired by the U.S. reached the base.

"The place of the fall of the other missiles is unknown," Konashenkov said, according to Russia's TASS news agency.

President Trump said he ordered the strikes early Friday local time in retaliation for a nerve gas attack by the regime of Syrian President Bashar Assad in the rebel-held town of Khan Sheikhoun in Idlib province that killed 86 people on Tuesday.

The Syrian army said the strikes made the United States a “partner” of the Islamic State, Jabhat al-Nusra and other terrorist organizations.

“At 3:42 a.m. today, the United States of America committed a blatant act of aggression targeting one of our air bases in the Central Region with a number of missiles, leaving 6 people martyred and a number of others injured and causing huge material damage,” the Syrian military said in a statement carried by the official Syrian Arab News Agency (SANA).

Assad allies Russia and Iran also condemned the U.S. strikes, saying they violated international law.

"It is an act of aggression under a completely far-fetched pretext," Russian Foreign Minister Sergey Lavrov said Friday, according to TASS. "This is reminiscent of the situation in 2003, when the U.S. and the U.K., along with some of their allies, invaded Iraq without the consent of the U.N. Security Council and in violation of international law," he said.

The Kremlin said it received advance warning from the U.S. about the strikes, the Associated Press reported. The British government also said it was informed about the strikes in advance.

Konashenkov said Russia will help Syria strengthen its air defenses to help “protect the most sensitive Syrian infrastructure facilities," the AP reported.

Iran said the U.S. action was "dangerous, destructive and violates the principles of international law.”

Iran’s Foreign Ministry spokesman, Bahram Ghasemi, said Iran condemned the strikes “regardless of the perpetrators and the victims” of the chemical weapons attack, and warned that it would “strengthen terrorists” and add to “the complexity of the situation in Syria and the region,” in comments carried by the semi-official ISNA news agency.

Russia claimed the deaths Tuesday were caused by a Syrian strike on a terrorist chemical weapons facility, but the U.S., other nations and human rights groups rejected that argument as baseless.

The 59 missiles, fired from the destroyers USS Porter and Ross in the eastern Mediterranean Sea, targeted the Shayrat Airfield in Homs province where Syria based the warplanes used in the chemical attack, according to Navy Capt. Jeff Davis, a Pentagon spokesman. The missiles destroyed aircraft, hardened hangars, ammunition supply bunkers, air defense systems and radar at the base.

"As always, the U.S. took extraordinary measures to avoid civilian casualties and to comply with the Law of Armed Conflict. Every precaution was taken to execute this strike with minimal risk to personnel at the airfield," Davis said in a statement.

The Syrian army said the U.S. striking the air base without determining what happened or who was responsible for the chemical attack “sends wrong messages to the terrorist organizations that would embolden them further to use chemical weapons in the future every time they suffer heavy losses in the battlefield," SANA reported.

Russian presidential spokesman Dmitry Peskov said Vladimir Putin believed that Washington’s “total disregard for the use of chemical weapons by terrorists only exacerbates the situation significantly.”

"Putin also sees the strikes on Syria by the U.S. as an attempt to divert the attention of the international community from numerous civilians casualties in Iraq. Washington’s move impairs the Russian-U.S. relations, which are in a deplorable state, substantially," Peskov added, according to TASS.

Trump said Assad "launched a horrible chemical attack on innocent civilians using a deadly nerve agent.

“Tonight I ordered a targeted military strike on the airfield in Syria from where the chemical attack was launched. It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons," Trump said Thursday.

The attack was the first conventional assault on another country ordered by the new president.

Saudi Arabia praised Trump’s “courageous decision” and blamed Assad’s government for the chemical weapons attack.

The Saudi Foreign Ministry said the missile launch ordered by Trump was the right response to “the crimes of this regime to its people in light of the failure of the international community to stop it,” the state-run Saudi Press Agency reported.

Israeli Prime Minister Benjamin Netanyahu also expressed his support for the strike.

"In words and actions President Trump sent a strong and clear response: The use of chemical weapons is unacceptable. Israel fully and unequivocally supports the president's decision and hopes the clear message will reverberate not only in Damascus but also in Tehran, Pyongyang and other places," Netanyahu said Friday, according to the Jerusalem Post.

Autopsies on three Syrians who died after being brought to Turkey for treatment suggest the banned nerve agent sarin was used in the chemical attack, the Turkish Health Ministry said.

Turkey, which also is involved in the fighting, has long pushed for Assad's ouster.

Contributing: Tom Vanden Brook and Gregory Korte