Sweden's path to Nato membership remains blocked by Turkey and Hungary ahead of a July summit in Vilnius where it hopes to join Nordic neighbour Finland as a full member of the alliance.
Finland, which applied together with Sweden, joined Nato in April, but Turkey continues to block Swedish membership citing security concerns. Ankara has said Sweden must crack down on anti-Turkey protests before getting a green light to join Nato.
Sweden has set its sights on joining at the alliance's July 11-12 summit and while it has strong support from other members including the US and more talks with Turkey are expected, there have been few clear signs of a breakthrough.
Russia's invasion of Ukraine in February last year convinced Sweden and Finland to ditch long-held policies of military non-alignment.
Both countries see Nato, with its collective defence clause, as the best way to ensure their security.
The majority of Nato members quickly ratified the applications, arguing that Finland - which shares a 1,300km border with Russia - and Sweden would strengthen the alliance in the Baltic.
Turkey gave approval for Finnish membership after initial objections. But Ankara says Sweden does not take its security concerns seriously and has not lived up to a bargain, struck in Madrid last year, that laid out a number of issues Stockholm needed to address.
Turkey has not budged despite Sweden implementing new anti-terror legislation in June that it believes should pave the way for accession.
Hungary has followed Turkey's lead in delaying ratification, which must be unanimous.
Why does Turkey object?
Stockholm has criticised Turkey for human rights abuses and over democratic standards, irking politicians in Ankara.
Turkey says Sweden harbours members of what it considers terrorist groups - a charge Sweden denies - and has demanded their extradition as a step toward ratifying Swedish membership.
Swedish courts have blocked some expulsions to Turkey.
Demonstrations held in Sweden have also raised Turkish ire.
In recent months, demonstrators in Stockholm have hung an effigy of Erdogan from a lamp-post. At other events, demonstrators waved flags showing support for the Kurdistan Workers' Party (PKK), which is deemed a terrorist group by Turkey and its Western allies, including Sweden.
Swedish Foreign Minister Tobias Billstrom has said the freedom to demonstrate is enshrined in the constitution while adding that "something that is legal is not always proper".
What is Hungary's beef with Sweden?
Hungary says Sweden has had a hostile attitude to Budapest for years. It is angry about Swedish criticism of Prime Minister Viktor Orban over the perceived erosion of rule of law. Orban denies such erosion. Unlike Turkey, Hungary does not have a list of demands, but says grievances need to be addressed before it can ratify Sweden's accession to Nato.
Swedish officials say they are perplexed by Hungary's stance and analysts have said the country is likely to follow Turkey's lead in the matter.
When will Turkey agree to Swedeish Nato membership?
Foreign minister Billstrom has been busy meeting a host of Nato allies in recent weeks to ensure Stockholm's membership bid remains top of the agenda, saying there is no "Plan B" beyond Sweden joining in Vilnius.
Sweden says it has implemented the Madrid agreement - including tougher anti-terrorism laws - and that some of Ankara's other demands are impossible to meet.
Erdogan has said the new laws are meaningless while supporters of the outlawed PKK are allowed to hold protests in Stockholm.
Yet Turkey has had previous run-ins with Nato allies and backed down. Elsewhere, support for Sweden is strong, with leaders from around Europe and the US calling on Ankara to move ahead with ratification.
Swedish and Turkish officials met on June 14 for what Sweden's chief negotiator characterised as good talks, are due to hold another high level meeting in Brussels before the Vilnius summit.
Is Sweden's security threatened by the delay?
Sweden has said its security position is better now than prior to its application to Nato. Sweden has received assurances of support from countries including the US, Britain and Germany.
Nato Secretary-General Jens Stoltenberg has said it would be inconceivable that the alliance would not support Sweden if it were threatened.
Sweden already cooperates closely with Nato and integration measures are moving forward. Sweden has a strong air force and a submarine fleet tailored to Baltic Sea conditions - a boost for Nato in the region.