Angela Merkel's brief visit to Warsaw on Tuesday marked the German leader's first trip to Poland since a populist government was elected there in 2015.

With trade between the two countries booming, Merkel's trip has been widely seen as a chance for Berlin and Warsaw to continue nurturing the slowly-improving diplomatic relations.

Following a 60-minute talk with Merkel, leader of the governing Law and Justice (PiS) party Jaroslaw Kaczynski said there was a "good atmosphere."

Kaczynski, a politician deeply distrustful of Germany, once said the chancellor's goal was to make Poland subordinate to its western neighbour.

Merkel meanwhile called on Poland's right-wing government on Tuesday to protect the rights of the political opposition as well as those of the justice system, trade unions and media, amid an investigation by the EU Commission into possible Polish violations of the rule of law.

Russia sanctions

In separate talks with Polish Prime Minister Beata Szydlo, Merkel addressed the ongoing conflict in Ukraine. The chancellor later told reporters that sanctions against Moscow over the ongoing conflict Ukraine cannot yet be lifted.

"The situation on the ground is still unacceptable," she said.

Merkel's comments came just hours after a telephone call with Russian President Vladimir Putin, in which she urged Putin to use his influence on separatists in eastern Ukraine to bring an end to almost three years of violence. The two agreed, however, on the need for new ceasefire efforts.

Poland against Nord Stream 2

Despite being largely on the same page when it comes to Russia, the controversial Nord Stream 2 project remains a contentious issue between Poland and Germany. Reiterating her country's stance on Tuesday, Szydlo said the Baltic Sea pipeline is "not acceptable to Poland."

The deal would see Russia's state controlled energy giant Gazprom extend its pipeline to Germany, bypassing Poland, the Baltic states and Ukraine.

EU reform

Also on the agenda in Warsaw was reform in the European Union. During the joint press conference, Szydlo said Poland is determined to further ties with Germany.

"I am confident that a good partnership between Poland and Germany is necessary for the success of the European project," Szydlo said.

"Poland and Germany ... have a huge role to play in the changes that are taking place in the Union," she added.

While Poland and Germany both favor stronger security at EU borders, Merkel said she was "cautious about demands for EU treaty change."

The German chancellor also warned against "exclusive clubs within the EU."

Trans-Atlantic relations

Two weeks into Donald Trump's presidency in the US, Merkel also addressed comments made by the newly-inaugurated president on Monday in which he said the US "strongly supports" NATO.

"What has been said of NATO by the president and by the defense and foreign ministers are very important statements and we will have the opportunity within NATO to meet and to talk about the future and the challenges," Merkel added.

Trump's most recent remarks regarding the trans-Atlantic alliance were a far cry from those made prior to his election in which he dismissed NATO as "obselete," sparking concerns that he would seek to withdraw the US from the alliance.

NATO defense ministers are due to meet with US Defense Secretary Jim Mattis for the first time next week, and again at the Munich Security Conference a week later.

During a phone call last month, Mattis told his German counterpart Ursula von der Leyen that the US was committed to the NATO alliance and US-Germany relations.

ksb/rt (Reuters, dpa)