Iran hosted officials from Ukraine in a second round of talks on Monday over compensation for a Kiev-bound passenger plane mistakenly shot down in January, state media reported.
Ukraine International Airlines Flight 752 crashed shortly after taking off from the Iranian capital's main airport on January 8.
The Islamic republic admitted days later that its forces accidentally shot down the plane, killing all 176 people on board, after firing two missiles amid heightened US-Iran tensions.
State news agency IRNA said the talks were held at the foreign ministry in Tehran and that they would continue until Wednesday.
The first round of negotiations were held in Kiev in July, with the Ukrainian authorities saying they were "cautiously optimistic" about the process.
Ukrainian deputy foreign minister Yevgeniy Yenin, who headed the delegation, met with Iran's foreign minister Mohammad Javad Zarif on Tuesday, after meeting with his deputy Mohsen Baharvand earlier in the day.
Zarif called the first round of talks held in Kiev "positive and constructive" and hoped that those in Tehran achieve their desired results, according to a statement by his ministry.
Yenin welcomed "Iran's decision to take full responsibility for bringing down the Ukrainian plane and its readiness to ensure the same compensation for all the relatives of the victims, regardless of their citizenship," said a separate statement by Ukraine's foreign ministry.
Yenin also emphasised the "need for an unbiased and objective investigation of the circumstances of the air disaster and called on the Iranian side to ensure access" to all of its elements, the statement added.
Iran's civil aviation authority has said the misalignment of an air defence unit's radar system was the key "human error" that led to the plane's downing.
Tehran's air defences had been on high alert at the time in case the US retaliated against Iranian strikes hours earlier on American troops stationed in Iraq.