His interview with German media comes as the number to have died in the Dnipro apartment blast is reported to have risen to 29. Russian fire struck the Ukrainian city on Saturday causing injury to a further 75 with at least 12 in a critical condition.
Kyiv has pushed for heavier weaponry from Western countries but nations have been reluctant to take any action that could further stoke Russia.
However, Mr Stoltenberg’s comments on Sunday night show that a new cause of action could be considered by NATO.
"The recent pledges for heavy warfare equipment are important -- and I expect more in the near future," he told the Handelsblatt daily.
“We are in a decisive phase of the war. Therefore, it is important that we provide Ukraine with the weapons it needs to win."
The German-based Ukraine Defence Contact Group, which coordinates arms supplies to Kyiv, is set to gather for a key meeting this week.
Europe has been steadily supplying weapons of greater power as the war has dragged on but this is the first time that it has been on the table that tanks could be provided.
Mr Stoltenberg said Russian president Vladimir Putin had made a mistake by attacking Ukraine and “overestimated the strength of his own armed forces”.
“We see their missteps, their lack of morale, the leadership problems, the poor equipment," he said.
But the Russians "have demonstrated that they are prepared to take heavy losses to achieve their goals," he added.
Valentyn Reznichenko, the head of the Dnipropetrovsk regional military administration, has shared news of the Dnipro attack on Telegram.
He wrote: “This afternoon, a 27-year-old woman was pulled out of the rubble. She is in intensive care with severe hypothermia. Doctors are fighting for her life.”
Mr Reznichenko added that 39 residents of the building were rescued from the rubble but the fate of a further 40 is unknown.