HALIFAX -- A top NATO official made the case for alliance unity Monday, citing what she said are "complex and challenging security issues" that include an "increasingly aggressive Russia."

Deputy secretary general Rose Gottemoeller focused on what she said was a "vast expansion and modernization" of the Russian military in an address before the NATO Parliamentary Assembly, which concluded four days of meetings in Halifax.

Gottemoeller singled out the development of Russia's new intermediate missile as "a particularly worrying aspect" because it is capable of delivering a nuclear warhead to the heart of Europe in minutes.

"This directly undermines one of the most important arms control treaties of the Cold War, the Intermediate Range Nuclear Forces Treaty (INF)," Gottemoeller said.

The 1987 treaty not only reduced the number of nuclear missiles held by both superpowers, but it also eliminated a whole class of weapons, Gottemoeller said.

"This new weapons system places the INF treaty at serious risk," she said.

Gottemoeller, who is American, reminded delegates that the U.S. has no new missiles of intermediate range in Europe.

She also pointed out that "nobody in this room wants a new arms race or new Cold War."

"Now is the time for dialogue but it is also the time for action by Russia to allay our very serious concerns. It is vital that when NATO talks we do so with one voice and a position of strength."

Gottemoeller said she believes a recently concluded exercise in Norway is proof of NATO's "unity of action." Exercise Trident Juncture was the largest alliance exercise since the Cold War, involving 50,000 troops from all 29 members along with Finland and Sweden.

"Our exercise ... sent a very clear message to all who may think to challenge the alliance," she said. "NATO stands ready to defend all of the allies against any threat."

The Halifax meeting brought together about 600 politicians from NATO member countries, as well as delegates from partner countries to discuss international security issues.

A wide range of hot-button topics were discussed during the weekend sessions, including Russian interference with democratic elections, NATO funding, and how terrorists use encrypted messages on the dark web.

Gottemoeller told the delegates that they play a central role in holding their individual governments to account and "holding their feet to the fire" when it comes to the money they spend and the actions they take in relation to security and to NATO.

"Your support for NATO within your parliaments, within budget discussions, and with your publics will make a big difference," said Gottemoeller. "There is nothing stronger than this alliance when it is united and when our publics are behind it. In that your support is essential."

Canada's defence minister, Harjit Sajjan, also addressed the assembly, telling it that Canada remains committed to the trans-Atlantic co-operation through the alliance.

Sajjan told the delegates that co-operation is needed more now than perhaps ever before in the face of military and non-traditional threats such as cyber attacks and hybrid tactics, which seek to shape or to change public opinion through various social media platforms.

"No single nation can face these challenges alone, so we come together in this extraordinary alliance to face them together," he said.

A series of nine resolutions from several committees were adopted by the assembly.

Among those was a resolution on burden sharing that urges all members to redouble efforts to move towards the two per cent of GDP guideline for defence spending by 2024.

Another welcomed the deepening of NATO-European Union cooperation in countering hybrid threats, while another called for increased cooperation in the Arctic to counter an increased Russian military buildup in the region.