Anders Fogh Rasmussen told Newsweek that despite Trump's public condemnation, increased U.S. activity has helped the alliance become stronger than it was at the start of the president's term.
Volodymyr Zelensky also thanked the U.S. for its continued support, noting he hoped to visit the White House soon for a meeting with Trump.
Trump has reportedly ordered his national security team to review some $250 million in military aid to Ukraine, which is fighting pro-Moscow separatists in the east of the country.
"I've never seen it before," the former GOP congressman said, pointing out that the attack came "in defense of an autocrat."
"Under no condition can we agree with this logic," European Council President Donald Tusk said.
On April 26, 1986, a failed safety test of the number 4 reactor at the nuclear power plant caused a huge explosion, releasing huge amounts of radiation into the environment.
The author replaced criticism of Putin with attacks on President Donald Trump and softened his description of Moscow's annexation of Crimea.
The parliamentary elections on Sunday saw Volodymyr Zelenskiy's party win an absolute majority.
Foreign Minister Sergei Lavrov also warned that proposed NATO expansion poses a threat to peace in Europe.
How can Ukraine prevent pro-Russian politics if voters prefer it? Another revolution. But revolutionary energy might be petering out.
New Safe Confinement seals the remains of the fourth reactor at the nuclear plant that was the site of the massive Chernobyl disaster in 1986.
Experts say that former President Poroshenko was held captive by his own rhetoric.
Russia has long expressed concern that its neighbors could become NATO members and that such developments could spark war.
Ukraine's government has long aspired to join NATO.
Experts say that Firtash's extradition could help usher in political reforms in Ukraine.
Russia's military preparation means "not a single hair on any Russian citizen's head would be harmed," Leonid Slutsky said.
Ukraine's new leader is meeting with key European leaders this week.
One military expert said Crimea is "bristling with missiles like a hedgehog."
President Donald Trump frequently reminds us that "all options are on the table" in enforcing U.S. policy, could that lead to war in Iran, North Korea, Syria, Ukraine or Venezuela?
"Most of the people say they decided to book after seeing this show. It's almost as though they watch it and then jump on a plane over."
As of Saturday, Sen. Chris Murphy said his letter to Republican leadership about Giuliani still stands.
"This isn't foreign policy—I'm asking them to do an investigation that they're doing already and that other people are telling them to stop."
Researchers loaded drones with radiation detectors to investigate the area devastated by the Chernobyl nuclear disaster.
Despite being one of the most radioactive areas on Earth, the Chernobyl Exclusion Zone attracts thousands of visitors each year.
A senior 2020 Trump campaign adviser used a 2015 video reportedly showing a Ukrainian rocket launch alongside a description of this weekend's deadly Gaza rockets.
Armies have been trying to harness the capabilities of marine animals like porpoises and sea lions for decades.
Vladimir Putin is making Russian passports more easily available to Ukrainians living in the self-proclaimed republics of Donetsk and Luhansk, where pro-Kremlin separatists have been battling Kiev forces.
"It is too early to talk about President Putin's offering his congratulations to Zelensky, as well as speaking about the possibilities of working together," a Kremlin spokesperson said about comedian-actor Volodymyr Zelensky, Ukraine's new president.
Researchers say the hacks appear to be authentic, but some of the allegations are impossible to verify.
Russia's appetite for Belarus is dictated by foreign policy considerations rather than domestic ones, but either way, Lukashenko might prove a tough nut to crack.