Weapons of mass destruction

Military personnel in College Street Car Park in Salisbury, Sunday March 11, 2018, as police and members of the armed forces probe the suspected nerve agent attack on Russian double agent Sergei Skripal, which took place on Sunday March 4. British health authorities said Sunday that small traces of contamination have been found in a restaurant and a pub in the English city of Salisbury, after a Russian ex-spy and his daughter were poisoned with a nerve agent. (Andrew Matthews/PA via AP)

People watch a TV screen showing North Korean leader Kim Jong Un and U.S. President Donald Trump, left, at the Seoul Railway Station in Seoul, South Korea, Friday, March 9, 2018. After months of trading insults and threats of nuclear annihilation, Trump agreed to meet with North Korean leader Kim Jung Un by the end of May to negotiate an end to Pyongyang's nuclear weapons program, South Korean and U.S. officials said Thursday. No sitting American president has ever met with a North Korea leader. The signs read: " Kim Jong Un understands that the routine joint military exercises between the South Korean and the United States must continue." (AP Photo/Ahn Young-joon)

Chinese State Councilor Yang Jiechi, right, meets with South Korea's national security director Chung Eui-yong, center, and South Korean ambassador to China Noh Young-min at the Diaoyutai State Guesthouse in Beijing Monday, March 12, 2018. (Etienne Oliveau/Pool Photo via AP)

People watch a TV screen showing North Korean leader Kim Jong Un and U.S. President Donald Trump, left, at the Seoul Railway Station in Seoul, South Korea, Friday, March 9, 2018. After months of trading insults and threats of nuclear annihilation, Trump agreed to meet with North Korean leader Kim Jung Un by the end of May to negotiate an end to Pyongyang's nuclear weapons program, South Korean and U.S. officials said Thursday. No sitting American president has ever met with a North Korea leader. The signs read: " Kim Jong Un understands that the routine joint military exercises between the South Korean and the United States must continue." (AP Photo/Ahn Young-joon)

People watch a TV screen showing North Korean leader Kim Jong Un and U.S. President Donald Trump, left, at the Seoul Railway Station in Seoul, South Korea, Friday, March 9, 2018. After months of trading insults and threats of nuclear annihilation, Trump agreed to meet with North Korean leader Kim Jung Un by the end of May to negotiate an end to Pyongyang's nuclear weapons program, South Korean and U.S. officials said Thursday. No sitting American president has ever met with a North Korea leader. The signs read: " Kim Jong Un understands that the routine joint military exercises between the South Korean and the United States must continue." (AP Photo/Ahn Young-joon)

People watch a TV screen showing North Korean leader Kim Jong Un and U.S. President Donald Trump, left, at the Seoul Railway Station in Seoul, South Korea, Friday, March 9, 2018. After months of trading insults and threats of nuclear annihilation, Trump agreed to meet with North Korean leader Kim Jung Un by the end of May to negotiate an end to Pyongyang's nuclear weapons program, South Korean and U.S. officials said Thursday. No sitting American president has ever met with a North Korea leader. The signs read: " Kim Jong Un understands that the routine joint military exercises between the South Korean and the United States must continue." (AP Photo/Ahn Young-joon)

People watch a TV screen showing North Korean leader Kim Jong Un and U.S. President Donald Trump, left, at the Seoul Railway Station in Seoul, South Korea, Friday, March 9, 2018. After months of trading insults and threats of nuclear annihilation, Trump agreed to meet with North Korean leader Kim Jung Un by the end of May to negotiate an end to Pyongyang's nuclear weapons program, South Korean and U.S. officials said Thursday. No sitting American president has ever met with a North Korea leader. The signs read: " Kim Jong Un understands that the routine joint military exercises between the South Korean and the United States must continue." (AP Photo/Ahn Young-joon)

In this photo released by the Oman News Agency, ONA, James Mattis, U.S. Defense Secretary Jim Mattis, right, shakes hands with Omani Brigadier Saleh bin Ahmed al-Hinai, Head of the Oman Military Protocols and Public Relations, at Seeb Air Base, northwest of Muscat, Oman, Sunday, March 11, 2018. Mattis on Sunday, warned the Syrian government not to use chemical weapons in its civil war. Mattis said Russia, which intervened militarily in Syria to support the Assad government, could be complicit in the civilian casualties. (Oman News Agency via AP)

This photo released by the Syrian official news agency SANA, Syrian Deputy Foreign Minister Faisal Mekdad, speaks during a news conference in Damascus, Syria, Saturday, March 10, 2018. Mekdad denied opposition charges that government forces used poison gas in their attacks on eastern Ghouta. Mekdad added that insurgents groups in the eastern Ghouta are preparing "to fabricate" more such attacks to blame the Syrian army. (SANA via AP)

This photo released by the Syrian official news agency SANA, Syrian Deputy Foreign Minister Faisal Mekdad, speaks during a news conference in Damascus, Syria, Saturday, March 10, 2018. Mekdad denied opposition charges that government forces used poison gas in their attacks on eastern Ghouta. Mekdad added that insurgents groups in the eastern Ghouta are preparing "to fabricate" more such attacks to blame the Syrian army. (SANA via AP)